Device and method for in vivo noninvasive magnetic manipulation of circulating objects in bioflows

ABSTRACT

A device and methods for the non-invasive manipulation and detection of target objects such as cells, pathogens, microparticles, and nanoparticles in vivo using an external magnetic field are described. In one aspect, a device and method for capturing and detecting intrinsically magnetic target objects or target objects labeled with at least one magnetic particle within the area of interest using an in vivo flow cytometer are described.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 12/334,217, entitled “Device and Method for In Vivo FlowCytometry Using the Detection of Photoacoustic Waves” filed on Dec. 12,2008, which is hereby incorporated by reference in its entirety.

GOVERNMENTAL RIGHTS IN THE INVENTION

This work was supported in part by the National Institutes of Healthgrants number R01EB000873, R21EB0005123, R01CA131164, R21CA139373, andR01EB009230, as well as the National Science Foundation grant numberDBI-0852737. The U.S. Government may have certain rights in thisinvention.

FIELD OF THE INVENTION

This application relates to a device and methods for the non-invasivemanipulation of target objects such as cells, pathogens, proteins,microparticles, and nanoparticles in vivo using an external magneticfield. In one aspect, this application relates to manipulating anddetecting intrinsically magnetic target objects or target objectslabeled with magnetic labeling compounds within the area of interestusing an in vivo flow cytometer.

BACKGROUND

Advancements in medical research have led to unprecedentedcharacterization of a plethora of factors involved in the developmentand progression of many diseases on cellular, subcellular, and molecularlevels. Using advanced measurement techniques such as reversetranscriptase polymerase chain reaction (RT-PCR), advanced in vitro flowcytometry, and microchip fluid technology, researchers have gainedvaluable insights with potential applications in the treatment of manydiseases.

A particularly challenging issue in medical research is the detectionand characterization of relatively rare cells such as tumor-initiatingcancer stem cells (CSCs), a treatment-resistant subclass of tumor cellsthought to be responsible for the growth and regrowth of primary andmetastatic tumors. The development of metastatic disease may be governedby the migration of CSCs from an existing tumor mass to remote locationsvia the circulatory or lymphatic system. The circulating tumor cells(CTCs) migrating within the circulatory or lymphatic systems typicallyinclude a relatively large number of differentiated tumor cells, and atiny subset of undifferentiated stem circulating tumor cells (stem CTCs)associated with metastatic disease. Because of the rarity of the stemCTCs in circulation, their detection is exceedingly difficult due tolimitations of existing measurement methods.

The sensitivity threshold of existing stem CTC assays, such as reversetranscriptase polymerase chain reaction (RT-PCR) assays, CellSearchsystem technology, in vitro flow cytometry, and microchip fluidtechnology is limited to approximately 1 cell per mL of sample due tothe relatively small volume processed by the assay's instrumentation,which is typically about 10 mL or less. This sensitivity is inadequateto reliably detect these rare stem CTCs, which may circulate inconcentrations of about 1 cell per 50 mL of blood or at even lowerconcentrations.

In vivo flow cytometry techniques, which detect cells as they circulatewithin the blood vessels of a living subject, overcome the sample volumelimitation, since these techniques are capable of processing the entireblood volume of the subject as it passes through a particular bloodvessel. However, for the detection of rare cells such as stem CTCs, thecell must pass though the area of interest of the instrumentation,typically a superficial blood vessel or lymph vessel. The amount of timerequired to observe a large volume of blood passing through the area ofinterest may be significant, especially when detecting andcharacterizing both the undifferentiated stem CTCs and thedifferentiated CTCs.

A need exists in the art to selectively enrich the concentration ofcells circulating in vivo in order to enhance the sensitivity of thedetection using in vivo flow cytometry techniques, among other needs.Such an enhancement would make possible the detection of relatively rarecells in a shorter amount of time, significantly increasing the celldetection sensitivity of the in vivo flow cytometry instrumentation. Theincreased cell detection sensitivity may allow for the earlier detectionand treatment of diseases related to circulating rare cells such as thedevelopment of metastatic diseases from circulating stem CTCs.

SUMMARY

Aspects of the present invention provide a device for the manipulationand detection of a magnetic target object within a moving biofluid of aliving organism such as blood, lymph or cerebrospinal fluid. The deviceincludes an in vivo flow cytometer for detecting the magnetic targetobject within an area of interest such as within a circulatory vesselthrough which the biofluid moves. The device also includes at least onemagnet situated from about 0.1 mm to about 20 cm of the area ofinterest, depending on magnetic field strength, which may range fromabout 0.1 Tesla to about 20 Tesla. The at least one magnet may produce amagnetic field that manipulates the magnetic target object within thearea of interest.

By using an external magnetic field to manipulate magnetic targetobjects, the magnetic target objects may be enriched, sorted, separated,captured, and/or immobilized as they are carried into the area ofinterest by the moving biofluid. For example, the magnetic targetobjects may be locally concentrated within the area of interest of thein vivo flow cytometer, significantly enhancing the detectionsensitivity of the device, in particular if the magnetic target objectsoccur at extremely low concentrations within the moving biofluid.

In one particular arrangement, the device may be used to detect thepresence of magnetic target objects within the moving biofluid of theliving organism using a method that includes situating at least onemagnet from about 0.1 mm to about 20 cm of an area of interest to alterthe movement of the moving magnetic target objects within a magneticfield produced by the at least one magnet. The method further includesdetecting the magnetic target objects using an in vivo flow cytometer.

In another aspect, a method is provided for detecting the presence oftarget cells within a moving biofluid of a living organism that includesinjecting magnetic nanoparticles conjugated with a first targetingmoiety into the moving biofluid to produce magnetic target cells thatinclude the magnetic particles attached to the target cells. In thismethod, photoacoustic contrast agents conjugated with a second targetingmoiety different than the first targeting moiety may be injected intothe moving biofluid to produce magnetic target cells labeled with thephotoacoustic contrast agents. The first and second targeting moietiesare different from each other, but both specifically target theattachment of the magnetic particle and the photoacoustic contrast agentto the same target cell type, which may be a cancer stem cell or othercell associated with a disease or disorder.

This method further includes situating at least one magnet from about0.1 mm to about 20 cm from an area of interest to alter the movement ofthe magnetic target cells within a magnetic field produced by the atleast one magnet, and detecting the magnetic target objects using an invivo photoacoustic flow cytometer. The method also includes subjectingthe magnetic target cells to an additional process that may includeremoving the target cells for biochemical or genetic analysis;non-invasive eradication using high-energy pulses chosen from laserpulses, microwave pulses, or ultrasound pulses; magnetic purging;mechanical removal; needle extraction; or any combination thereof.

Additional objectives, advantages and novel features will be set forthin the description which follows or will become apparent to thoseskilled in the art upon examination of the drawings and the detaileddescription which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of a photoacoustic in vivo flow cytometry method.

FIG. 2 includes two schematic diagrams illustrating an in vivo flowcytometry device with an external magnet attached near the area ofinterest (FIG. 2A) and an in vivo flow cytometry device that includes amagnet integrated into the optical module (FIG. 2B).

FIG. 3 shows the oscilloscope trace recordings of PA signals: (A) fromblood flow in a rat ear vessel with diameter of 50 μm, (B) from skinsurrounding a rat ear vessel before dye injection, (C) from blood flowin a rat ear vessel 5 min after the injection of Lymphazurin, and (D)from the skin surrounding a rat ear vessel measured 20 min after dyeinjection.

FIG. 4 shows the PA signal detected from the monitoring of the bloodflow in a 50-μm rat ear microvessel with diameter after intravenousinjection of Lymphazurin dye in the tail vein.

FIG. 5 shows the PA signal from circulating GNR in 50-μm rat mesenterymicrovessels as a function of post-injection time.

FIG. 6 is a graph of the normalized number of circulating GNR in bloodmicrovessels of the rat mesentery as a function of post-injection timeand a dashed curve showing averaged data (N=3).

FIG. 7 is a graph of the normalized number of circulating S. aureus inblood microvessels of the mouse ear as a function of post-injectiontime, for bacteria labeled using two different contrast substances, ICGdye and CNT.

FIG. 8 is a graph of the normalized number of circulating E. coli inblood microvessels of the mouse ear as a function of post-injectiontime.

FIG. 9 shows the PA spectra of 50-μm diameter veins in the mouse ear(empty circles), conventional absorption spectra of the B16F10 mousemelanoma cells with strong pigmentation (upper dashed curve) and weakpigmentation (lower dashed curve), spectra normalized using PA signalsfor the single mouse melanoma cells with strong pigmentation (blackcircles) and weak pigmentation (black squares), and absorption spectrafor pure Hb and HbO₂ (fragments of solid curves in the spectral range630-850 nm).

FIG. 10 is a graph showing the frequencies of circulating mouse melanomacells (B16F10) detected with label-free PAFC in 50-μm mouse ear veins,with a flow velocity of 5 mm/s, in mice with low (A) and high (B)melanin pigmentation as a function of post-injection time.

FIG. 11 is a summary of the PA signal rates from single melanoma cellsdetected in a mouse ear lymph microvessel 5 days after tumorinoculation.

FIG. 12 is a summary of the PA signal rates from a single RBC (whitebar) and lymphocytes (black bars) detected by PAFC in the lymph flow ofrat mesentery.

FIG. 13 shows oscilloscope traces of the two-wavelength, time-resolveddetection of PA signals from: (A) necrotic lymphocytes labeled with goldnanorods absorbing 639 nm laser pulses, (B) apoptotic lymphocyteslabeled with gold nanoshells absorbing 865 nm laser pulses, and (C) liveneutrophils labeled with carbon nanotubes absorbing both the 639 nm andthe 865 nm laser pulses.

FIG. 14 shows oscilloscope traces of the two-wavelength, time-resolveddetection of PA signals from: (A) melanoma cells absorbing 865 nm and639 nm laser pulses, and (B) red blood cells absorbing 865 nm and 639 nmlaser pulses.

FIG. 15 is a summary of the PA signal rates from melanin particlesdetected in a mouse ear lymph microvessel 2 hours after injection.

FIG. 16 is a summary of the PA signal rates from single melanoma cellsdetected in a mouse ear lymph microvessel 4 weeks after tumorinoculation.

FIG. 17 is a summary of the PA signal amplitude generated by quantum dotmarkers as a function of laser fluence.

FIG. 18 is a summary of the PA signal amplitude generated by quantum dotmarkers as a function of the number of laser pulses.

FIG. 19 is a summary of the PA signal amplitudes from a capillary overthe 20 minutes following the injection of magnetic nanoparticles.

FIG. 20 is a summary of the PA signal rates from single melanoma cellsand bacteria cells labeled with magnetic nanoparticles detected in amouse ear capillary 30 minutes after injection.

FIG. 21 is a summary of the PA signal rates from melanoma cells labeledwith magnetic nanoparticles before and after the application of amagnetic field, detected in a mouse ear capillary 20 minutes afterinjection.

FIG. 22 is a summary of the PA signal rates from bacterial cells labeledwith magnetic nanoparticles before and after the application of amagnetic field, detected in a mouse ear capillary 20 minutes afterinjection.

FIG. 23 includes fluorescent microscopic images of a suspension ofmagnetic nanoparticles conjugated with targeted antibodies. FIG. 23A isa fluorescent microscopic image of the suspension with no externalmagnetic field applied. FIG. 23B is a fluorescent microscopic image ofthe same suspension after the end of a magnet is attached to the top ofthe slide cover.

FIG. 24 includes non-linear photothermal (PT) signals obtained from asuspension of magnetic nanoparticles conjugated with targetedantibodies. FIG. 24A is a non-linear photothermal (PT) signal obtainedfrom the suspension with no external magnetic field applied. FIG. 24B isa non-linear photothermal (PT) signal obtained from the same suspensionafter the end of a magnet is attached to the top of the slide cover.

FIG. 25 includes fluorescent microscopic images of a single cancer celllabeled using magnetic nanoparticles conjugated with targetedantibodies. FIG. 25A is a fluorescent microscopic image of the labeledcancer cell with no external magnetic field applied. FIG. 25B is afluorescent microscopic image of the same labeled cancer cell after theend of a magnet is attached to the top of the slide cover.

FIG. 26 includes non-linear photothermal (PT) signals obtained from asingle cancer cell labeled using magnetic nanoparticles conjugated withtargeted antibodies. FIG. 26A is a non-linear photothermal (PT) signalobtained from the labeled cancer cell with no external magnetic fieldapplied. FIG. 26B is a non-linear photothermal (PT) signal obtained fromthe same labeled cancer cell after the end of a magnet is attached tothe top of the slide cover.

FIG. 27 is a schematic illustration of a conjugated magneticnanoparticle.

FIG. 28 is a schematic illustration of a conjugated gold nanotube.

FIG. 29 are estimated photoacoustic spectra showing the PA signals of amagnetic nanoparticle, a gold nanotube, and blood background signals asa function of laser pulse wavelength.

FIG. 30 includes microscope images of a single cancer cell incubatedwith unconjugated magnetic nanoparticles (FIG. 30A) and of a singlecancer cell incubated with conjugated magnetic nanoparticles (FIG. 30B).

FIG. 31 contains fluorescent microscope images of a single cancer cellincubated with fluoroscein-stained unconjugated gold nanotubes (FIG.31A) and a single cancer cell incubated with fluoroscein-stained,folate-conjugated gold nanotubes (FIG. 31B).

FIG. 32 is a schematic illustration of a PAFC system modified to providethe capability to attach a magnet near the area of interest of the PAFCsystem.

FIG. 33 is a summary of the PA signal rates produced by three differentsamples at a range of laser fluences: a suspension of magneticnanoparticles, a suspension of cells labeled with magneticnanoparticles, and a suspension of cells labeled with magneticnanoparticles in an external magnetic field.

FIG. 34 is a summary of the PA signal rates from samples of goldnanotubes and magnetic nanoparticles spiked into mouse blood at a rangeof nanoparticle concentrations.

FIG. 35 is a schematic illustration of a PAFC flow simulation system.

FIG. 36 includes non-linear photothermal (PT) signals obtained fromlabeled cancer cells (FIG. 36A) and from the surrounding suspensionmedium (FIG. 36B) using a PAFC flow simulation system.

FIG. 37 includes fluorescent microscopic images of cancer cells labeledwith conjugated magnetic nanoparticles in the vicinity of a magnetshowing the labeled cancer cells suspended in PBS at a flow velocity of0.5 cm/s (FIG. 37A), the labeled cancer cells with additional conjugatedmagnetic nanoparticles at flow velocities of 0.1 cm/s (FIG. 37B) and 5cm/s (FIG. 37C).

FIG. 38 is a summary of the capture efficiency (the number of cells orparticles captured at a flow velocity as a percentage of the number ofcells or particles captured at 0.1 cm/s.

FIG. 39 is a summary of the PA signal rates produced by circulating goldnanotubes and magnetic nanoparticles in a mouse ear vein after aninitial injection of the nanoparticles into the tail vein of the mouse.

FIG. 40 is a summary of the PA signal rates produced by circulatingcancer cells that were labeled with nanoparticles either in vitro or invivo measured from a mouse abdominal vein an initial injection of thelabeled cells (in vitro) or after an initial injection of unlabeledcancer cells followed by a separate injection of conjugatednanoparticles (in vivo) into the tail vein of the mouse.

FIG. 41 is a summary of the PA signal rates from circulating tumor cellsin a mouse abdominal vein measured at 2, 3, and 4 weeks of tumordevelopment. The circulating tumor cells were labeled in vivo usingconjugated magnetic nanoparticles and gold nanotubes.

FIG. 42 is a summary of the PA signal rates from circulating tumor cellsin an abdominal vein after one week of tumor development. Thecirculating tumor cells were labeled with magnetic nanoparticles in vivoand an external magnetic field was applied near the area of interest inthe abdominal vein 20 minutes after initial injection of conjugatedmagnetic nanoparticles.

FIG. 43 is a summary of the PA signal rates from circulating tumor cellsin an abdominal vein after two weeks of tumor development. Thecirculating tumor cells were labeled with magnetic nanoparticles invivo. PA signals were measured before the application of a magneticfield, one hour after the initial application of an external magneticfield, and after the removal of the magnetic field.

FIG. 44 is a diagram of a magnetic cuff.

FIG. 45 is a diagram of a magnetic cuff secured to an extremity of anorganism.

FIG. 46 is a diagram of a magnetic cuff that includes an array of twomagnets, shown secured to an extremity of an organism.

FIG. 47 is a diagram of a minimally invasive needle device showninserted into an organism to situate a magnet in close proximity to acirculatory vessel.

FIG. 48 is a diagram of an extracorporeal shunt inserted into anorganism to direct the flow of a biofluid outside of the organism and toreturn the biofluid back into the organism.

FIG. 49 is a diagram of an array of magnets enriching the concentrationof magnetic target objects within an area of interest.

FIG. 50 is a diagram of an array of magnets spatially sorting a mixtureof magnetic target objects within an area of interest.

FIG. 51 is a diagram of a single magnet spatially sorting a mixture ofmagnetic target objects within an area of interest.

FIG. 52A is a diagram of an extracorporeal shunt. FIG. 52B is aphotograph of an extracorporeal shunt attached to a white rat. FIG.52C-FIG. 52E are microscope images of the blood flow through theextracorporeal shunt at magnifications of 4×, 20×, and 100×,respectively.

Corresponding reference characters indicate corresponding elements amongthe views of the drawings. The headings used in the figures should notbe interpreted to limit the scope of the claims.

DETAILED DESCRIPTION

A device for detecting the presence of target objects within a movingbiofluid of a living organism is provided in one aspect. This deviceincorporates the manipulation of magnetic target objects within amagnetic field applied to the area of interest of an in vivo flowcytometer, resulting in a detection sensitivity that is significantlyenhanced relative to previously described in vivo flow cytometrysystems. The manipulation of the target objects may include but is notlimited to locally enriching the concentration of target objects withinthe area of interest, capturing or immobilizing the target objectswithin the area of interest, spatially separating or sorting two or moretarget objects within the area of interest, concentrating the targetobjects within a selected region of the biofluid, or any combinationthereof. The target objects may be intrinsically magnetic, or the targetobjects may be rendered magnetic by the attachment of magnetic particlesto the target cells. The magnetic particles specifically bind to thedesired target particles due to the conjugation of the magneticparticles with targeting moieties such as antibodies or ligand proteinsthat are characteristic components of the target objects. The targetobjects may be biomarkers, pathogens such as viruses or bacteria, normalcells such as circulating red blood cells, or abnormal cells such ascirculating cancer stem cells. The device may further be capable ofnon-invasively eradicating the target objects captured within the areaof interest once the identity of the target objects has been confirmedusing the detection device.

In another aspect, a method of using the device to detect the presenceof target objects within a moving biofluid of a living organism isprovided. The method may include labeling the target object by injectingmagnetic particles conjugated to targeting moieties into the movingbiofluid, as well as injecting contrast agents conjugated to secondtargeting moieties into the moving biofluid, producing a target objectlabeled with both a magnetic particle and a contrast agent. The type ofcontrast agent may be any contrast agent compatible with the detectionsensors of the in vivo flow cytometry device, including but not limitedto photoacoustic contrast agents, ultrasound contrast agents, andfluorescent markers. Once the targeting agent has been labeled, a magnetis situated in the vicinity of the area of interest to alter themovement of the labeled target objects, and the in vivo flow cytometrydevice is used to detect the labeled target objects within the area ofinterest. The target objects may also be removed for further biochemicalor genetic analysis, or may be eradicated using a technique includingbut not limited to overheating by excessive photoabsorption effects.

The device and methods of using the device, as well as the targetobjects, magnetic particles and contrast agents used to label the targetobjects are described in detail below.

I. Description of Device

In various aspects, the device may include an in vivo flow cytometer andat least one magnet, described below.

a. In Vivo Flow Cytometer

In an aspect, the device includes an in vivo flow cytometer that may beany known in vivo flow cytometer, including, but not limited to, thephotoacoustic flow cytometry device (PAFC) described in U.S. patentapplication Ser. No. 12/334,217, the contents of which are incorporatedherein in their entirety. Although any in vivo flow cytometer may beincluded in the device, the device will be described herein assuming theinclusion of a PAFC.

Referring to FIG. 1, the PAFC detects target objects in a movingbiofluid by generating a laser pulse at step 201 and directing the laserenergy resulting from the laser pulse to the area of interest containingthe circulating target cell at step 202. The target cell, which mayeither possess intrinsic photoacoustic (PA) properties or may be labeledwith a PA contrast agent, emits a PA signal that is detected at step203. The detected PA signal may be amplified at step 204, recorded atstep 205, and analyzed at step 206 to determine the presence of thetarget cell in the area of interest.

Referring to FIG. 2A, in one aspect the device 100 includes an in vivoflow cytometer 120 used to detect the presence of target objects 140within the area of interest 132 of a moving biofluid 502. In thisaspect, the in vivo flow cytometer 120 may be a PAFC that includes apulsed laser 122 capable of emitting laser energy 126 ranging betweenwavelengths of about 400 nm and about 2500 nm, and may further includean optical module 124 to convert the wavelength, pulse duration, or bothwavelength and pulse duration emitted by the pulsed laser 122 to desiredvalues. For example, a Raman shifter may be used to deliver a probepulse having a wavelength and pulse duration that are different from thepump pulse received from the pulsed laser 122. In addition, the in vivoflow cytometer 120 may further include optical elements 130 such aslenses or optic fibers to direct the laser energy 126 to the targetobjects 140. The in vivo flow cytometer 120 may also include at leastone ultrasound transducer 150 to detect photoacoustic waves 142 emittedby the target objects 140.

In other aspects, the in vivo flow cytometer 120 may utilize one or moreknown detection methods to detect the target objects 140. Non-limitingcell detection methods suitable for use by an in vivo flow cytometer 120include photoacoustic methods, photothermal methods, fluorescentmethods, Raman and other scattering methods, and any combinationthereof.

As shown in FIG. 48, the in vivo flow cytometer 120 may detect targetobjects 140 in a moving biofluid 502 flowing through an extracorporealshunt 500. The extracorporeal shunt 500 directs the moving biofluid 502from an afferent circulatory vessel 504 such as an artery within theintegument 506 of an organism to a circulatory bypass tube 508 outsideof the organism. The target objects 140 may be detected as they movethrough an area of interest 132 by the in vivo flow cytometer 120. Themoving biofluid 502 is returned back into an efferent circulatory vessel510 such as a vein within the integument 506 of an organism. A pump 516such as a peristaltic pump may be further included to move the biofluid502 through the circulatory bypass tube 508. A high speed highresolution imaging mode optical system 518 may be used to providevisualization of individual moving cells at single cell level, as wellas to guide the placement of the elements of the in vivo flow cytometer120. Other aspects of the extracorporeal shunt 500, such as themanipulation of the movement of the target objects 140 using magnets110G and 110H, are discussed in further detail below.

If the target objects 140 are immobilized within the area of interest132, either within the organism or within an extracorporeal shunt 500,other methods and devices in addition to an in vivo flow cytometer 120may be used to detect and characterize the target objects 140.Non-limiting examples of suitable devices for the detection andcharacterization of immobilized target objects 140 include MRI, CT, PET,ultrasound, and conventional or fluorescent microscopy devices.

b. Magnet

The device 100 may further include a magnet 110 situated in closeproximity to the area of interest 132 such that the magnetic fieldinduced by the magnet 110 alters the movement of the target objectsflowing past the area of interest 132, as shown in FIG. 2A. The targetobjects 140 may be intrinsically magnetic or may be labeled withattached magnetic particles, rendering them susceptible to the forcesinduced by a magnetic field produced by the magnet 110. The magneticfield may manipulate the target objects 140 within the area of interest132. Non-limiting examples of manipulations of the target objects 140include: immobilization, enrichment, sorting, separating, concentrationwithin a selected region of the biofluid, and combinations thereofwithin the area of interest 132.

The magnet 110A may also be incorporated into the in vivo flow cytometer120, as shown in FIG. 2B. In this aspect, the laser energy 126 may bedirected to the area of interest 132 using an optic fiber 104 thatincludes a focusing tip 106. The material of the magnet 110A may form achannel 102 through which the laser fiber 104 may pass in order tosituate the focusing tip 106 in a laser pulse location that isessentially coincident with the corresponding magnetic field produced bythe magnet 110A.

As shown in FIG. 48, one or more magnets 110H-110G may be situated inclose proximity to a circulatory bypass tube 508. The target objects maybe captured, sorted, or otherwise manipulated by a magnetic fieldproduced by the one or more magnets 100G-110H within the area ofinterest 132 in which the in vivo flow cytometer 120 detects the targetobjects.

The magnet 110 may be any existing permanent magnet or electromagnetcapable of producing a steady or pulsed magnetic field at the magnetsurface of at least 0.1 T. In other aspects, the magnetic field strengthat the magnet surface may be from about 0.1 T to about 7 T, from about0.1 T to about 0.5 T, from about 0.25 T to about 0.75 T, from about 0.5T to about 1 T, from about 0.75 T to about 1.5 T, from about 1 T toabout 2 T, from about 1.5 T to about 2.5 T, from about 2 T to about 4 T,from about 3 T to about 5 T, from about 4 T to about 6 T, from about 5 Tto about 7 T, from about 6 T to about 8 T, from about 7 T to about 9 T,from about 8 T to about 10 T, from about 9 T to about 11 T, from about10 T to about 12 T, from about 11 T to about 13 T, from about 12 T toabout 14 T, from about 13 T to about 15 T, from about 14 T to about 16T, from about 15 T to about 17 T, from about 16 T to about 18 T, fromabout 17 T to about 19 T, and from about 18 T to about 20 T. Thestrength of the magnetic field at the magnetic surface may be selectedto be sufficiently strong to capture the target objects 140 movingthrough the area of interest 132. The strength of the magnetic fieldsufficient for the capture of moving target objects 140 may beinfluenced by any one or more of at least several factors including, butnot limited to, the size of the circulatory vessel through which thebiofluid 500 may flow, the depth of the circulatory vessel relative tothe skin surface of the organism, the flow speed of the biofluid 500through the area of interest 132, the separation distance between themagnet 110 and the area of interest 132, the duration of the magneticpulse produced by a pulsed electromagnet, the intrinsic magneticproperties of the target object 140, and the amount of magnetic materialused to label the target object 140, among other possible factors.

The magnet 110 may be constructed using any known magnetic material,including but not limited to hematite (Fe₂O₃), magnetite (Fe₃O₄),manganese-zinc ferrite (Mn_(a)Zn_((1-a))Fe₂O₄), nickel-zinc ferrite(Ni_(a)Zn_((1-a))Fe₂O₄), barium oxide, strontium oxide, and combinationsthereof. In an aspect, the magnet may be a cylindricalneodymium-iron-boron (NdFeB) magnet with Ni—Cu—Ni coating. Any knownelectromagnet may be used including but not limited to resistiveelectromagnets and superconducting magnets.

In an aspect, the magnet 110 may be situated at a distance ranging fromabout 50 μm to about 20 cm from the area of interest 132, depending onthe strength of the magnet 110. In other aspects, the magnet 110 may besituated at a distance ranging from about 50 μm to about 200 μm, fromabout 100 μm to about 300 μm, from about 200 μm to about 400 μm, fromabout 300 μm to about 500 μm, from about 400 μm to about 600 μm, fromabout 500 μm to about 700 μm, from about 600 μm to about 800 μm, fromabout 700 μm to about 900 μm, from about 800 μm to about 1 mm, fromabout 0.9 mm to about 1.1 mm, from about 1 mm to about 1.4 mm, fromabout 1.2 mm to about 1.6 mm, from about 1.4 mm to about 1.8 mm, fromabout 1.6 mm to about 2.0 mm, from about 1.8 mm to about 2.2 mm, fromabout 2 mm to about 2 cm, from about 1 cm to about 3 cm, from about 4 cmto about 6 cm, from about 5 cm to about 7 cm, from about 6 cm to about 8cm, from about 7 cm to about 9 cm, from about 8 cm to about 10 cm, fromabout 9 cm to about 11 cm, from about 10 cm to about 15 cm, and fromabout 14 cm to about 20 cm from the area of interest 132. In anotheraspect, the magnet 110 may be attached externally to the integumentsurface of the organism in close proximity to the area of interest 132.

In another aspect, the magnet 110 may be situated in close vicinity ofthe area of interest 132 using a minimally invasive needle deliverydevice. In yet another aspect, the magnet 110 may be situated in closevicinity of the area of interest 132 using a magnet 110 mounted in acatheter device. An illustration of a minimally invasive needle device400 in one particular aspect is shown in FIG. 47. In this device 400,the magnet 110F may be situated within a needle 402 which may beinserted into the organism 404 so that the magnet 110F is in closeproximity to a circulatory vessel 308, shown here in cross-section.

In still yet another aspect, the magnet 110 may be placed in closeproximity to the area of interest 132 using a magnetic cuff thatincludes the magnet attached to a securing cuff. A schematic drawing ofa magnetic cuff 300 is illustrated in FIG. 44. The magnetic cuff 300includes a securing cuff 302 with an attached magnet 100B. The magneticcuff 300 may also include a means of securing the cuff 302 such as aVELCRO hook strip 304 and loop strip 306. As shown in FIG. 45, themagnetic cuff 300A may be situated such that the magnet 110C is in closeproximity to a circulatory vessel 308, and secured around an extremity310 of the organism such as an arm to hold the magnet 110C in place.Once secured, the magnetic cuff 300 may be worn by the organism in orderto alter the movement of the magnetic target objects within thecirculatory vessel 308. While wearing the magnetic cuff 300, theorganism may move without disturbing the placement of the magnet 110Crelative to the circulatory vessel 308. In an aspect, the magnet 110Cmay further contain a channel 102A through which an optic fiber 104 (notshown) may be threaded in order to direct the laser pulses used for invivo flow cytometry without removing or repositioning the magnet 110C.

The securing cuff 302 may be of any known design including a flexiblestrip secured using Velcro straps, a belt strap, releasable buckles,releasable clamps, or any other known securing means. The magnetic cuffmay be worn by an organism for a period of time ranging from about 30minutes to about 12 hours prior to the detection of the target objects140 using the in vivo flow cytometer 120. The magnetic cuff may besecured around any extremity of the organism, including, but not limitedto, an arm, a leg, a finger, a toe, a wrist, an elbow, a shoulder, anankle, a knee, a hip, and a neck. In an additional aspect, the magnetmay be attached to the external integument of the organism using anadhesive device including but not limited to an adhesive bandage oradhesive tape.

In an additional other aspect, the magnet 110 may be a pulsed magnetincluding but not limited to an MRI pulsed electromagnet to hold thetarget objects 140 within the area of interest 132. In this aspect,rather than capturing the target objects 140 using a time-invariantmagnetic field, the pulsed magnet may produce a series of magnetic fieldpulses within the area of interest 132 that periodically alters thevelocity of movement of the target objects 140 within the biofluid 500.For example, the magnetic pulses produced by the pulsed magnet mayreverse the velocity of movement of the target objects 140 so that theymove upstream into the area of interest 132 for the duration of themagnetic pulse, and then the velocity of the target objects 140 maygradually reverse direction and start to move downstream and away fromthe area of interest 132 before the next magnetic pulse returns thetarget objects to the area of interest 132.

In still yet another aspect, the magnet 110 may include two or moremagnets 110 arranged in an array to capture the target objects 140within the area of interest 132; the array of magnets 110 may have anydesired geometrical arrangement. For example, as shown in FIG. 49, thearray of magnets may include two or more magnets 110I-100J arrangedalong the length of a circulatory vessel through which the biofluid 500moves. In this example, the most upstream magnet 110I may only becapable of slowing the velocity of the target objects 140 relative tothe surrounding biofluid movement, and the more downstream magnet 110Jmay then be capable of capturing the slowed target objects 140. Inanother example (not shown), the two or more magnets 110I-110J arrangedalong the length of the circulatory vessel may be of sufficient strengthto capture the target objects 140 and immobilize the target objects 140within the volume of the circulatory vessel that is situated between thetwo or more magnets 110 in the array.

Referring to FIG. 50, an array of magnets 110I-110J may also provide thecapability to sort and capture two or more different target objects 140Aand 140B. In this aspect, the more upstream magnet 110I may produce amagnetic field of sufficient strength to capture target objects 140A,which may be more susceptible to capture due to one or more factorsincluding but not limited to a smaller size or mass relative to targetobject 140B, a smaller concentration of magnetic materials relative totarget objects 140B, a smaller size of magnetic particles attached tothe target objects 140A relative to target objects 140B, or a smallernumber of magnetic particles attached to the target objects 140Arelative to target objects 140B. Further, the more downstream magnet100J may produce a magnetic field of sufficient strength to capturetarget objects 140B, which were slowed relative to the flow of thebiofluid by the more upstream magnet 100I. As a result, target objects140A and 140B may be spatially separated and captured using an array ofmagnets 110I-110J as shown in FIG. 50. In another aspect, a single longmagnet 110K may be used in place of the array of magnets in order tospatially separate and capture two or more different target objects 140Aand 140B, as shown in FIG. 51.

A magnetic cuff 300B that incorporates two magnets 110D and 100E isillustrated in FIG. 46. In this aspect, the two magnets 110D and 110Eare situated along the length of circulatory vessel 308 in closeproximity to the vessel 308. The securing cuff 302 may then be securedaround the extremity 310 of the organism to hold the magnets 110D and110E in place relative to the circulatory vessel 308.

The target objects 140 may be concentrated near the area of interestusing methods other than applied magnetic fields. For example, targetobjects 140 possessing a larger diameter than the surrounding cells maybe concentrated by reducing the cross-sectional area of the lumen of acirculatory vessel through which the biofluid 500 flows in the vicinityof the area of interest 132 using gentle mechanical pressure on thetissue surrounding the circulatory vessel, thereby retaining the largerdiameter target objects 140, while allowing the surrounding cells withsmaller diameter than the target objects 40 to flow away unimpeded fromthe area of interest 132. The amount of pressure applied to the tissuesurrounding the circulatory vessel may be regulated using cell detectionrates obtained using the in vivo flow cytometer 120 at different levelsof mechanical pressure.

II. Target Objects

The device 100 may be used to detect target objects 140 in a movingbiofluid of a living organism. The devices and methods discussed hereinmay be used on any organisms that possess a moving biofluid.Non-limiting examples of living organisms that possess a moving biofluidinclude vertebrates such as mammals, reptiles, birds, amphibians, andfish; plants; fungi; mollusks; insects; arachnids; annelids; arthropods;roundworms; and flatworms. Non-limiting examples of suitable movingmammalian biofluids include blood, lymph, cerebrospinal fluid, urine,chyme, cytosol, tears, and interstitial fluid. Other non-limitingexamples of non-mammalian moving biofluids include hemolymph andintracellular fluid.

The moving biofluid and target objects 140 may flow through acirculatory vessel, defined herein as any fluid-containing space withina living organism through which the flow of a biofluid is directed.Non-limiting examples of circulatory vessels in vertebrate livingorganisms include blood or lymphatic vessels. Other non-limitingexamples of circulatory vessels include capillaries, arterioles,venules, arteries, veins, lymphatic vessels, hyphae, phloem, xylem,hemocoels, and sinuses. The circulatory vessels may be located in manydifferent organs and tissues, including, but not limited to, skin, lip,eyelid, interdigital membrane, retina, ear, nail pad, scrotum, lymphnodes, brain, breast, prostate, lung, colon, spleen, liver, kidney,pancreas, heart, testicular, ovarian, lung, uterus, bone, bone marrow,peritoneum, skeletal muscle, smooth muscle, and bladder tissues.

The area of interest through which a moving biofluid flows may be at adepth ranging from about 10 m to about 15 cm below the surface of theintegument of a living organism. If the moving biofluid is detectedwithin a circulatory vessel or an extracorporeal shunt, the diameter ofthe circulatory vessel or shunt may range from about 10 μm to about 2cm.

In another aspect, the target objects 140 may be magnetic target objectsin order to be susceptible to the magnetic forces produced by the magnet110 within the area of interest 132. In this aspect, magnetic targetobjects 140 may include intrinsically magnetic target objects, targetobjects labeled with magnetic particles, and any combination thereof.Non-limiting examples of target objects 140 suitable for detection bythe device 100 include unlabeled biological cells having intrinsicmagnetic properties such as red blood cells and iron-containingsiderophilic bacteria, biological cell products having intrinsicmagnetic properties, unbound contrast agents having intrinsic magneticproperties, unbound magnetic particles, biological cells labeled usingmagnetic particles, biological cell products or active pharmaceuticalcompounds labeled using magnetic particles, and any combination thereof.The target objects 140 may be endogenous or exogenous biological cellsor cell products that may possess intrinsic magnetic properties or maybe labeled using magnetic particles. Non-limiting examples of suitablecells or cell products include normal, apoptotic and necrotic red bloodcells and white blood cells; aggregated red blood cells or white bloodcells or clots; infected cells; inflamed cells; stem cells; dendriticcells; platelets; metastatic cancer cells resulting from melanoma,leukemia, brain cancer, breast cancer, colon cancer, prostate cancer,ovarian cancer, pancreatic cancer, and testicular cancer; bacteria;viruses; fungal cells; protozoa; microorganisms; pathogens; animalcells; plant cells; and leukocytes activated by various antigens duringan inflammatory reaction and combinations thereof. Non-limiting examplesof biological cell products include products resulting from cellmetabolism or apoptosis, cytokines or chemokines associated with theresponse of immune system cells to infection, exotoxins and endotoxinsproduced during infections, specific gene markers of cancer cells suchas tyrosinase mRNA, p97, MelanA/Mart1 produced by melanoma cells, PSAproduced by prostate cancer, and cytokeratins produced by breastcarcinoma.

In yet another aspect, the target objects 140 that are unlabeledbiological cells may possess intrinsic magnetic properties due to theinclusion of magnetic materials such as iron in the composition of theunlabeled biological cells. For example, red blood cells contain ironwithin the enclosed hemoglobin, rendering the unlabeled red blood cellssusceptible to capture by magnetic forces of sufficiently high magneticfield strength. Other non-limiting examples of metal-containingcell-specific markers that confer at least some degree of intrinsicmagnetism to an unlabeled cell include hemoglobin (Hb), HbH, HbO₂,metHb, HbCN, HbS, HbCO, HbChr, myoglobins, cytochromes, catalase,porphyrins, chlorophylls, and combinations thereof.

In still yet another aspect, the target objects 140 may be labeled usingattached magnetic particles to render the target objects 140 susceptibleto capture by the magnetic field within the area of interest 132. Themagnetic particles may be nanoparticles or microparticles ranging insize from about 5 nm to 10 μm. Non-limiting examples of suitablemagnetic particles include ferromagnetic materials such as iron, nickel,cobalt, iron oxides, nickel oxides, cobalt oxides, alloys of rare earthmetals, and any mixture or alloy thereof. In an additional aspect, themagnetic particles may include a magnetic material and an externalcoating of a biocompatible and/or non-toxic material including but notlimited to gold, silver, titanium, and platinum. In order to selectivelylabel the target objects 140, the magnetic particles may be conjugatedwith a cell-specific targeting moiety that has a high affinity for someunique feature of the target object 140 such as a cell membrane markeror receptor. Non-limiting examples of targeting moieties suitable forconjugation with a magnetic particle include antibodies, proteins,folates, ligands for specific cell receptors, receptors, peptides,viramines, wheat germ agglutinin, and combinations thereof. Non-limitingexamples of suitable ligands include ligands specific to folate,epithelial cell adhesion molecule (Ep-CAM), Hep-2, PAR, CD44, epidermalgrowth factor receptor (EGFR), as well as receptors of cancer cells,stem cells receptors, protein A receptors of Staphylococcus aureus,chitin receptors of yeasts, ligands specific to blood or lymphatic cellendothelial markers, as well as polysaccharide and siderophore receptorsof bacteria.

Two or more different magnetic particles conjugated with differentcell-specific targeting moiety may be used to label each of two or moredifferent cell types with one of the magnetic particles. For example,one cell type may be labeled with larger magnetic particles and anothercell type may be labeled with smaller magnetic particles in order tofacilitate the spatial sorting of the two cell types within the area ofinterest, as shown in FIGS. 50-51.

In an additional aspect, the magnetic particles may be eliminatedrelatively quickly from the circulation of the organism. For example, ifthe magnetic particles are magnetic nanoparticles conjugated totargeting moieties with an affinity to circulating tumor cells, theunbound conjugated magnetic nanoparticles in circulation may bind to thecirculating tumor cells within about 15 minutes. Any unbound conjugatedmagnetic particles remaining in circulation only add to any backgroundnoise in the signals used to detect the circulating tumor cells by thein vivo flow cytometer 120. In this aspect, magnetic particles may beused that are eliminated a time period ranging from about 15 minutes toabout 60 minutes.

In an additional other aspect, in order to enhance the detectionsensitivity of the device 100, the target objects 140 may be labeledusing a contrast agent to enhance a signal. Any existing contrast agentmay be used that is compatible with the detection method used by the invivo flow cytometer 120. Non-limiting examples of suitable contrastagents include an ultrasound contrast agent, a photoacoustic contrastagent, a hybrid contrast agent, a fluorescent contrast agent, a Ramancontrast agent, an MRI contrast agent, a superconductivity quantuminterference device contrast agent, a PET contrast agent, and a CTcontrast agent. Non-limiting examples of specific contrast agentsinclude indocyanine green dye, melanin, fluoroscein isothiocyanate(FITC) dye, Evans blue dye, Lymphazurin dye, trypan blue dye, methyleneblue dye, propidium iodide, Annexin, Oregon Green, Cy3, Cy5, Cy7,Neutral Red dye, phenol red dye, AlexaFluor dye, Texas red dye, goldnanospheres, gold nanoshells, gold nanorods, gold cages, carbonnanoparticles, prefluorocarbon nanoparticles, carbon nanotubes, carbonnanohorns, magnetic nanoparticles, quantum dots, binary gold-carbonnanotube nanoparticles, multilayer nanoparticles, clusterednanoparticles, liposomes, liposomes loaded with contrast dyes, liposomesloaded with nanoparticles, micelles, micelles loaded with contrast dyes,micelles loaded with nanoparticles, microbubbles, microbubbles loadedwith contrast dyes, microbubbles loaded with nanoparticles, dendrimers,aquasomes, lipopolyplexes, nanoemulsions, polymeric nanoparticles, andcombinations thereof.

Hybrid contrast agents may include nanoparticle complexes ormicroparticle complexes that function simultaneously as contrast agents,depending on the particular materials and geometry of the magneticparticles. Non-limiting examples of suitable hybrid contrast agentsinclude gold-magnetic complexes, quantum dot-magnetic complexes, carbonnanotube-magnetic complexes, radionucleotide-magnetic complexes, surfaceenhanced resonance scattering-magnetic complexes, or any combinationthereof. In addition, the contrast agents described previously may alsosimultaneously function as magnetic particles depending on the materialsincluded in the contrast agents.

The multilayer nanoparticles used as photoacoustic contrast agents forthe target objects 140 may include two or more layers of materials withoptical, thermal, and acoustic properties that enhance the PA signals142 emitted by the target objects 140. Non-limiting examples of theeffects of the multilayered nanoparticles on the PA pulses 142 emittedby the target objects 140 labeled with the multilayered nanoparticlesinclude enhancing absorption of the laser pulse energy, increasingthermal relaxation time, increasing acoustic relaxation time, increasingthe coefficient of thermal expansion, decreasing the coefficient ofthermal diffusion, decreasing the local speed of sound near the targetobject 140, decreasing the threshold of bubble formation of the targetobject 140 and combinations thereof.

Exogenous target objects 140 such as unbound contrast agents andexogenous unlabeled biological cells may be introduced into the biofluid500 of the organism perenterally, orally, intradermally, subcutaneously,or by intravenous or intraperitoneal administration. For example,unbound magnetic particles conjugated to targeting moieties may beinjected intravenously into the moving biofluid 500 within a circulatoryvessel in order to label the target objects 140.

To further increase the contrast between PA signals 42 or originatingfrom the target objects 40 and the background PA signals fromsurrounding cells and tissues, a variety of approaches may be used. Theorganism may be exposed to hyperoxic or hypoxic atmospheric conditionsto induce different levels of oxygenation, which in turn alters thelight absorption properties of the red blood cells. The osmolarity ofthe biofluid 500 may be altered by injecting hypertonic or hypotonicsolutions into the biofluid 500, thereby causing physical swelling orshrinking of surrounding cells, and further altering the lightabsorption characteristics of the surrounding cells. The hematocrit ofthe biofluid 500 may be altered by the injection of a diluting solutioninto the biofluid 500, thereby reducing the density of surrounding cellsin the biofluid 500, and the resulting light absorption characteristicsof the surrounding cells.

III. Methods of Manipulating and Detecting Target Objects

In an aspect, the device 110 may be used to detect the presence of atarget object 140 with a detection sensitivity ranging from about 1 toabout 100 target objects per L of biofluid. A method of detecting thepresence of magnetic target objects 140 within a moving biofluid of aliving organism may include situating at least one magnet 110 in closeproximity an area of interest to alter the movement of the magnetictarget objects 140 within a magnetic field produced by the at least onemagnet 110. In this aspect, the captured magnetic target objects 140 maybe detected using the in vivo flow cytometer 120.

As described previously, the magnetic target objects 140 may beintrinsically magnetic objects, or non-magnetic objects with attachedmagnetic particles. For example, the magnetic target object may be acirculating cancer stem cell labeled using an iron oxide nanoparticleconjugated with a protein ligand of a cell receptor characteristic ofthe circulating cancer stem cell.

In an aspect, the target objects 140 may be labeled using magneticparticles conjugated with a targeting moiety by injecting the conjugatedmagnetic particles into the moving biofluid within the organism. In thisaspect, the conjugated magnetic particles may take a period of timeranging from about 15 minutes to about 60 minutes to selectively bind tothe target objects 140. In addition, unbound magnetic particles aretypically cleared from circulation about 20 minutes to about 60 minutesafter injection, so that any magnetic particles captured after this timeperiod are most likely to be labeled magnetic target objects 140.

In another aspect, the target objects 140 may be labeled using magneticparticles conjugated with a targeting moiety by injecting the conjugatedmagnetic particles into the biofluid 502 moving through anextracorporeal shunt 500 via an injection port 512, as shown in FIG. 48.Further, the method of labeling the target objects 140 within theextracorporeal shunt 500 may reduce the interaction time between themagnetic particles and the biofluid and other cells not targeted by themagnetic particles, resulting in a reduced risk of toxicity. To furtherreduce the risk of toxicity, a second, more powerful magnetic array 514or other means of recapturing the unbound magnetic particles may beincluded to reclaim the magnetic particles prior to the reintroductionof the biofluid 502 into the vein 510 of the living organism.

In order to verify that the captured magnetic particles are attached totarget objects 140, the target objects 140 may be additionally labeledwith a contrast agent chosen from an ultrasound contrast agent, aphotoacoustic contrast agent, a fluorescent contrast agent, a Ramancontrast agent, an MRI contrast agent, a PET contrast agent, or a CTcontrast agent, depending on the method of detection used by the in vivoflow cytometer 120. The contrast agents may also be conjugated to asecond targeting moiety to facilitate the specific binding of thecontrast agent to the target object 140. To avoid interfering withspecific binding of the magnetic particles to the target objects 140 thesecond targeting moiety is chosen to be a different compound from thetargeting moiety conjugated to the magnetic particles.

The target objects 140 may be additionally labeled with a contrast agentconjugated with a second targeting moiety by injecting the conjugatedcontrast agents into the biofluid 500 of the organism. Further, theinjection containing the conjugated contrast agents may be administeredat a different time than the injection containing the conjugatedmagnetic particles at the same or different locations. Alternatively,the injection containing the conjugated contrast agents may beadministered at a different time than the injection containing theconjugated magnetic particles at the same or different locations. Theconjugated contrast agents may also be combined with the conjugatedmagnetic particles and administered as a single injection.

One or more magnets 110 may be situated in close proximity to the areaof interest 132 as described herein after labeling the target objects140 using the magnetic particles and/or contrast agents in order tomanipulate the target objects 140 within the area of interest 132. Themagnets 110 may be an integrated component of the in vivo flow cytometer120, or may be separate components. The magnets 110 or may be supportedin a separate item such as a magnetic cuff 300, in a minimally invasiveneedle device 400 or catheter device, or in an extracorporeal shunt 500,as described herein.

The magnets may be used to manipulate the labeled target objects 140 fora capture period ranging from about 10 minutes to about 2 hours. Thelength of the capture period may be selected based on one or more ofseveral possible factors including but not limited to the effectivenessof the one or more magnets 110 at capturing the labeled target objects140 based on magnetic field strength, flow speed of the biofluid, themagnetic dipole of the labeled target object 140, and the amount of timetaken for the entire volume of biofluid to pass through the area ofinterest. The capture period in one particular implementation may be thetime for the entire biofluid volume within the organism to pass throughthe area of interest 132. In this aspect, essentially all labeled targetobjects within the moving biofluid may be captured and detected withinthe area of interest 132, resulting in significantly enhanced detectionsensitivity.

For example, if the area of interest 132 is a human artery or veinhaving a diameter ranging from about 2 mm to about 3 mm, the total bloodvolume of 5 L may circulate through the artery or vein within about onehour, particularly of an artery or vein in close proximity to the heartis chosen and if few alternative flow paths exist between the targetartery or vein and the heart. Accordingly, the capture period may beselected to be about one hour in order to capture essentially alllabeled target objects 140 circulating in the blood volume within thearea of interest 132.

If the one or more magnets 110 are incorporated into the in vivo flowcytometer 120, the organism may be immobilized or otherwise constrainedsuch that the area of interest 132 is kept in close proximity to the oneor more magnets 110. If the one or more magnets 110 are included in amagnetic cuff 300, the patient may wear the magnetic cuff independentlyof the in vivo flow cytometer 120, as illustrated in FIG. 45 and FIG. 46and described herein, and may further move freely until the capturedtarget objects 140 are detected by the in vivo flow cytometer 120. Invarious aspects, the magnetic cuff 300 may be removed just prior to thedetection of the captured target objects 140, the magnetic cuff 300 maybe designed to be worn while the captured target objects 140 aredetected by the in vivo flow cytometer 120. For example, if the in vivoflow cytometer 120 is a photoacoustic flow cytometer (PAFC) similar tothe PAFC illustrated in FIG. 2B, the magnetic cuff 300 may be designedas illustrated in FIG. 45 to include a channel 102A through the magnet110C so that an optic fiber 104 (not shown) may be inserted through themagnetic cuff 300A during detection of the captured target objects 140(not shown) by the in vivo flow cytometer 120 (not shown).

Although various aspects of the method for capturing and detectingtarget objects 140 have been described in terms of a photoacousticdetection methods, other detection methods may be used eitherindividually or in combination. In various aspects the in vivo flowcytometer 120 may incorporate elements to detect conventional and Ramanscattering of the laser pulses by the target objects 140, photothermaleffects induced by laser pulses on the target objects 140, and thefluorescence of the target objects 140 induced by absorbed laser pulses.

Once the target objects 140 within the area of interest 132 have beendetected by the in vivo flow cytometer 120, the target objects 140 maybe removed from the area of interest 132 using known microsurgicaltechniques and subsequently analyzed using techniques including but notlimited to biochemical, histological, or genetic analysis techniques inan aspect. For example, the analysis may be used to identify thephenotype and metastatic activity of captured cells in order to assessthe stage of a disease, such as cancer, to provide information todetermine an appropriate course of treatment, or to assess the efficacyof a previously-administered course of treatment.

In another aspect, the target objects 140 may be purged from the movingbiofluid using the extracorporeal shunt 500 shown in FIG. 48. In thisaspect, target objects 140 such as stem circulating tumor cells may bemagnetically labeled by injecting magnetic particles conjugated with atargeting moiety into the biofluid 502 via the injection port 512. Thetargeting moieties specifically bind to the target objects 140 and theattached magnetic particles cause the target objects 140 to be capturedwithin the magnetic field in the area of interest 132 produced bymagnets 110G and 110H. Once the target objects 140 are detected withinthe area of interest 132 by the in vivo flow cytometer 120, the targetobjects 140 may be removed from the area of interest 132 through awithdrawal port 516. For example, the magnetic purging of theundesirable target objects 140 including but not limited to toxins, highconcentration drugs, sickle cells, or tumor cells may be accomplishedusing a means such as the extracorporeal shunt 500 shown in FIG. 48.

The captured target objects 140 may also be eliminated usingnon-invasive techniques. For example, if the in vivo flow cytometer 120is a photoacoustic flow cytometer, the target objects 140 may beeliminated by illuminating the target objects 140 using laser pulseshaving a pulse wavelength and laser fluence chosen to cause theselective destruction of the target objects 140. Because the absorptionof the laser pulses of the target objects 140 is much higher than thesurrounding cells and tissue, the laser fluence may be increased beyondthe level normally used for detection to levels that selectively damagethe target objects 140 without harming the surrounding cells andtissues. Non-limiting examples of target objects 40 that may beselectively eliminated include tumor cells, bacteria, viruses, clots,thromboses, plaques, and combinations thereof.

In various aspects, the method of manipulating and detecting targetobjects 140 in the moving biofluid 500 of an organism may be used for avariety of medical applications, including but not limited to monitoringof circulating cancer cells for the early diagnosis and treatment ofmetastasis, inflammations, sepsis, immunodeficiency disorders, strokes,and heart attacks.

EXAMPLES

The following examples illustrate the invention.

Example 1 In Vitro Photothermal (PT) Imaging was Used to Determine theEffect of Laser Energy Levels on Laser-Induced Cell Damage to BloodCells and Subsequent Cell Viability

To determine whether the laser pulses produced during in vivo flowcytometry caused any significant damage to cells or tissues of theorganism, the following experiment was conducted. The laser-induceddamage threshold of single cells was evaluated as a function of thepumped-laser energy levels at a range of wavelengths using establishedmethods (Zharov and Lapotko 2005, Lapotko and Zharov 2005). In vitromeasurements of specific changes in photothermal (PT) images and PTresponses from individual cells were used to determine cell damage.During the PT imaging, individual cells were illuminated with a pulse oflaser light at a specified energy level and wavelength. After absorbingthe energy of the laser pulse, the short-term temperature of the cellincreased by as much as 5° C. The laser-induced temperature-dependentrefractive heterogeneity in the vicinity of cells caused defocusing of acollinear He—Ne laser probe beam (model 117A; Spectra-Physics, Inc.; 633nm, 1.4 mW) that illuminated the cell immediately after the initiallaser pulse. This defocusing caused a subsequent reduction in the beam'sintensity at its center, which was detected with a photodiode (C5658;Hamamatsu Corp.) through a 0.5-mm-diameter pinhole.

PT measurements were performed in vitro using mouse blood cells insuspension on conventional microscope slides. To simulate blood flowconditions, a flow module fitted with a syringe pump-driven system (KDScientific, Inc.) was used with glass microtubes of different diametersin the range of 30 μm to 4 mm that provided flow velocities of 1-10cm/sec, which were representative of the diameters and flow rates ofanimal microvessels.

Individual cells flowing through the glass microtubes were exposed to an8 ns burst of laser light in a 20-m circular or elongated beam at avariety of wavelengths ranging between 420 nm and 2300 nm. At eachwavelength of the initial laser pulse, the laser fluence, defined as theenergy contained in the laser beam, was varied between 0.1 mJ/cm² and1000 J/cm². Damage to the cells was determined by assessing the changesin the PT imaging response of cells to laser pulses of increasingfluence. In addition, cell viability after exposure to laser energy wasassessed using a conventional trypan blue exclusion assay. Cellulardamage was quantified as ED50, the level of laser fluence at which 50%of the measured cells sustained photodamage in vitro. The ED50 valuesmeasured for rat red blood cells (RBC), white blood cells (WBC) and K562blast cells using laser pulses in the visible light spectrum aresummarized in Table 1. The ED50 values measured for rat red blood cells(RBC) and white blood cells (WBC) using laser pulses in thenear-infrared (NIR) light spectrum are summarized in Table 2.

TABLE 1 Photodamage thresholds for single rat blood cells in the visiblelight spectrum. Photodamage threshold Wavelength of ED50 (J/cm²) laserpulse Rat K562 (nm) Rat RBC Rat WBC blast cell 417 1.5 12 36 555 5 42 90

TABLE 2 Photodamage thresholds for single rat blood cells in near-IRspectral range. Photodamage Wavelength of threshold ED50 laser pulse(J/cm²) (nm) Rat RBCS Rat WBCs 740 6.9 21.7 760 6.8 780 17.7 152 80017.5 219 820 28.0 251 840 43.5 860 43.8 730 880 76.5 900 69.4 920 77.7357 960 33.5 48.8

In the visible spectral range, the relatively strong light-absorbingRBCs sustained cell damage at much lower intensities of laser energy,resulting in ED50 values that were about an order of magnitude lowerthan the ED50 values measured for WBC or K562 blasts. In the NIRspectral range, where most cells, including RBC, have minimalabsorption, cells did not sustain damage until much higher laser energylevels compared to the energy levels at which cellular damage occurredto cells exposed to laser energy in the visible spectrum. The damagethresholds (ED50) for RBCs and WBCs in the spectral range of 860-920 nmwere more than one order magnitude higher compared to those in thevisible spectrum as shown in Tables 1 and 2.

The results of this experiment established the levels of laser energy atwhich laser-induced cellular damage may occur. In the NIR spectrum, inwhich cells exhibited the strongest photoacoustic effects, the damagethresholds are several orders of magnitude above the maximum safetylevel of approximately 20-100 mJ/cm² set by ANSI safety standards. Thus,photoacoustic flow cytometry may be performed in vivo with little riskof cell or tissue damage.

Example 2 Prototype In Vivo Photoacoustic Flow Cytometry System Used toDetect Contrast Dye Circulating in Mice

The following experiment was conducted to demonstrate the feasibility ofin vivo photoacoustic flow cytometry (PAFC) for real-time, quantitativemonitoring in the blood circulation of a conventional contrast agent,Lymphazurin. In this experiment, a prototype PAFC system was used todetect Lymphazurin circulating in the blood vessels of a mouse ear.

The prototype PAFC system was built on the platform of an Olympus BX51microscope (Olympus America, Inc.) and a tunable optical parametricoscillator (OPO) pumped by a Nd:YAG laser (Lotis Ltd., Minsk, Belarus).The general layout of the PAFC system is shown in FIG. 2. Laser pulseshad an 8 ns pulse width, a regular repetition rate of 10 Hz with theability to provide short-term pulses at 50 Hz, and a wavelength in therange of 420-2,300 nm. Laser energy was directed to the blood vesselsusing a conventional lens, or an optical fiber. PA waves emitted by thecells were detected by ultrasound transducers (unfocused Panametricsmodel XMS-310, 10 MHz; focused cylindrical Panametrics model V312-SM, 10MHz, focused lengths of 6 mm, 12 mm, and 55 mm; and customized resonancetransducers), and the ultrasound transducer outputs were conditioned byan amplifier (Panametrics model 5662, bandwidth 50 kHz-5 MHz;Panametrics model 5678, bandwidth 50 kHz-40 MHz; customized amplifierswith adjustable high and low frequency boundaries in the range to 50-200KHz and 1-20 MHz, respectively; resonance bandwidth of 0.3-1.0 MHz). Theamplifier output signals were recorded with a Boxcar data acquisitionsystem (Stanford Research Systems, Inc.) and a Tektronix TDS 3032Boscilloscope, and were analyzed using standard and customized software.The Boxcar data acquisition technique provided averaging of the PA wavesfrom cells in the blood vessels, and discriminated the PA waves frombackground signals from surrounding tissue on the basis of thedifference in time delays between the two signals. The signals from theoscilloscope screen were recorded with a digital camera (Sony, Inc.) andvideo camera (JVC, Inc.).

A high-speed computer (Dell Precision 690 workstation with a quadcoreprocessor, 4 GB of RAM and Windows Vista 64 bit operating system) anddigitizer (National Instruments PCI-5124 high speed digitizer) were usedto acquire the PA signal data from the PAFC device. National Instrumentssoftware (Labview Version 8.5 and NI Scope Version 3.4) was used tocontrol the digitizer and create a data logging user interface. Thehardware and supporting program were capable of collecting data at arate of 200 megasamples per second, corresponding to a time resolutionof 5 ns.

A laser beam with a circular cross section and a diameter ofapproximately 50 m, a wavelength of 650 nm, and a fluence of 35 mJ/cm²was used to illuminate the flow in the blood vessels. The 650 nmwavelength used was near the wavelength of maximum absorption ofLymphazurin, the contrast dye used in this experiment, and wellseparated from the wavelengths of maximum absorption of other bloodcomponents. Navigation of the laser beams was controlled withtransmission digital microscopy (TDM) at a resolution of approximately300 nm using a Cascade 650 CCD camera (Photometrics).

All in vivo experiments described below were performed using a nudemouse ear model. PAFC detection was performed using relativelytransparent, 270 μm thick mouse ears with well-distinguished bloodmicrovessels. The ear blood vessels examined were located at a depth of30-100 μm, had diameters in the range of 30-50 μm, and blood velocitiesof 1-5 mm/sec. After undergoing anesthesia using ketamine/xylazine at adosage of 50/10 mg/kg, each mouse was placed on a customized heatedmicroscope stage, together with a topical application of warm water,which provided acoustic matching between the transducer and mouse ear.

The contrast dye used for the experiments described below wasLymphazurin, a contrast agent commonly used for the delineation oflymphatic vessels. A 1% solution of Lymphazurin (Isosulfan Blue) waspurchased from Ben Venue Labs Inc., USA.

After anaesthetizing each mouse and placing the mouse on the microscopestage as described above, 200 μl of a 1% aqueous solution of Lymphazurinwas injected into the tail vein of the mouse.

PAFC measurements of the circulating dye were performed at a laser pulsewavelength of 650 nm. FIG. 3 shows oscilloscope traces of PAFC signalsfrom the blood vessels and surrounding tissues in the rat ear before andafter injection with Lymphazurin. Prior to injection, the maximum 240 mVPA signals from blood vessels, shown in FIG. 3A, were approximately 1.5times higher than the 160 mV PA background signals from surroundingtissue, shown in FIG. 3B. Maximum PA signals from the blood vessel afterdye administration, shown in FIG. 3C, increased approximately three-foldover pre-injection levels. The PA signals from tissue around vesselsafter dye injections, shown in FIG. 3D, gradually increasedapproximately 2.5-fold over pre-injection levels during the first 15-20minutes, and then remained relatively constant for the next 1-1.5 hours,possibly due to the passage of the Lymphazurin out of the blood vesselsand into nearby lymphatic vessels.

FIG. 4 summarizes the maximum PAFC signals from Lymphazurin compared tobackground PAFC signals from the blood vessels, observed for one hourafter the injection of Lymphazurin. As shown in FIG. 4, continuousmonitoring of PA signals from the ear blood microvessels revealed arapid appearance of Lymphazurin in the blood flow within a few minutesafter injection, followed by clearance of Lymphazurin from the bloodover the next 50 minutes.

The results of this experiment demonstrated that the prototype PAFCsystem exhibited sufficient sensitivity to detect the presence ofultrasonic contrast dyes in circulation.

Example 3 Prototype In Vivo Photoacoustic Flow Cytometry System Used toDetect Nanoparticles Circulating in Rats

To demonstrate the sensitivity of a prototype in vivo photoacoustic flowcytometry (PAFC) system described in Example 2 an experiment wasconducted using the prototype PAFC system to detect nanoparticlesintravenously injected into the tail veins of rats.

The in vivo measurements in this experiment were performed using the ratmesentery model. The rat (White Fisher, F344) was anesthetized usingketamine/xylazine at a dosage of 60/15 mg/kg, and the mesentery wasexposed and placed on a heated microscope stage, and bathed in Ringer'ssolution at a temperature of 37° C. and a pH of 7.4. The mesenteryconsisted of transparent connective tissue of 7-15 μm thickness, and asingle layer of blood and lymph microvessels.

The nanoparticles used in this experiment were gold nanorods (GNR),obtained from the Laboratory of Nanoscale Biosensors at the Institute ofBiochemistry and Physiology of Plants and Microorganisms in Saratov,Russia. On the basis of TEM and dynamic light scattering analyses, theGNR were estimated to be approximately 15 nm in diameter andapproximately 45 nm in length on average. The nanoparticles were usedeither uncoated or functionalized using thiol-modified polyethyleneglycol (PEG) (Liao and Hafner 2005).

A 250-μL suspension of GNR with a concentration of 10¹⁰ particles/ml wasinjected into the tail veins of three rats, followed by the continuousmonitoring of PA signals measured from 50-μm diameter blood vessels inthe rat mesentery using the PAFC system described in Example 2. PAFCmeasurements were taken using a laser fluence of 100 mJ/cm², a laserbeam diameter of approximately 50 μm, and a laser wavelength of 830 nm,near the maximum absorption of the GNR.

Uncoated GNR were rapidly cleared from the blood circulation within 1-3minutes preferentially by the reticuloendothelial system (data notshown). After PEGylated GNR injection, strong fluctuating PA signalsappeared with amplitudes significantly exceeding the PA backgroundsignals from blood vessels within the first minute and continued for14-25 minutes, depending on the individual animal. In addition, the PAbackground signal from the blood vessel increased approximately 1.5-2times above the pre-injection background levels, reaching a maximumlevel between four and nine minutes after injection, as shown in FIG. 5.

The averaged PA signals from three animals, measured for 15 minutesafter injection with GNR suspensions, are summarized in FIG. 6. Themaximum rate of individual PA signals per minute, representing thenumber of GNR in circulation, was achieved approximately 5 minutes afterinjection, with a gradual decrease in the signal rate over the next 10minutes.

The results of this experiment demonstrated that the prototype PAFCsystem possessed sufficient spatial and temporal resolution tocontinuously monitor the circulation of nanoparticles as small as 15 nmin diameter. In addition, the prototype PAFC system was sufficientlysensitive to track fluctuations of the concentration of circulatingparticles from the time that they were injected to the time that theparticles were cleared from circulation.

Example 4 Prototype In Vivo Photoacoustic Flow Cytometry System Used toDetect S. aureus Bacteria Circulating in Mice

To demonstrate the ability of the prototype photoacoustic flow cytometry(PAFC) system to detect bacteria cells in vivo under biologicalconditions, the following experiment was conducted. The prototype PAFCsystem, previously described in Example 2, was used to measure S. aureusbacteria in the circulation of nude mice.

The mouse ear model described in Example 2 was used for all measurementsof circulating bacteria in the experiment. Because the endogenous lightabsorption of S. aureus bacteria was relatively weak compared to theabsorption of other blood components in the NIR spectral range, thebacteria were labeled with the NIR-absorbing contrast substancesindocyanine green dye (ICG) and carbon nanotubes (CNT), due to theirrelatively high labeling efficiency and low toxicity (data not shown).

The S. aureus bacterium strain designated UAMS-1 was isolated from apatient with osteomyelitis at the McClellan Veterans Hospital in LittleRock, Ark., USA. The strain was deposited with the American Type CultureCollection and is available as strain ATCC 49230. UAMS-1 was cultured intryptic soy broth and grown aerobically for 16 h at 37° C. Cells wereharvested by centrifugation, resuspended in sterile PBS and incubatedwith Indocyanine Green (ICG) dye (Akom Inc., USA) or carbon nanotubes(CNT) as described below.

Before incubation, ICG dye was filtered through a 0.22 μm pore sizefilter. A 150-μl aliquot of bacteria in suspension was incubated with375 μg of ICG in 150 μl of solution for 30 min at room temperature andthen for 2 h at 37° C. Labeled bacteria were centrifuged at 5,000 rpmfor 3 min and the resulting pellet was resuspended in PBS.

Single-walled and multi-walled carbon nanotubes (CNT) were purchasedfrom Carbon Nanotechnologies Inc. (Houston, Tex.) and Nano-lab Inc.(Newton, Mass.), respectively. The CNT samples used in this study wereprocessed using known methods (Kim et al. 2006). The average length anddiameter of the single-walled CNT were 186 nm and 1.7 nm respectively,and the average length and diameter of the multi-walled CNT were 376 nmand 19.0 nm respectively.

CNT solutions were treated with five cycles of 1.5 min of ultrasound ata power of 3 W followed by 0.5 min of rest, for a total of 10 minutes ofinterrupted ultrasound. A 150-μl aliquot of bacteria in suspension wasincubated with 150 μl of CNT solution for 30 minutes at room temperaturefollowed by 2 additional hours of incubation at room temperature.Labeled bacteria were centrifuged at 10,000 rpm for 5 min and theresulting pellet was resuspended in PBS.

Labeled 100-μl suspensions of S. aureus bacteria at a concentration of5×10⁵ cells/ml were injected into the mouse's tail vein, and theclearance of the labeled bacteria was monitored using PAFC measurementstaken from 50-μm diameter microvessels in the ears of mice. Laser energywas delivered at a wavelength of 805 nm for the S. aureus that waslabeled with ICG, and at a wavelength of 850 nm for the S. aureus thatwas labeled with CNT. For both label types, the laser energy wasdelivered at a beam diameter of approximately 50 μm and at a fluenceranging between 20 and 50 mJ/cm².

S. aureus bacteria labeled with ICG and CNT contrast substances yieldedsimilar results, summarized in FIG. 7. After injection of labeled S.aureus, PAFC detected a rapid appearance of bacteria in the ear bloodmicrovessels within the first minute, followed by a steady eliminationof the bacteria from the blood circulation over the next 3-5 minutes.Periodic PAFC monitoring of mice blood vessels over the next few daysrevealed that very rare bacteria labeled with CNT or possibly unattachedCNT continued to appear at an average rate of one PA signal every threeminutes, and the labeled bacteria or CNT was not completely cleared fromcirculation until about 60 hrs after the initial injection (data notshown).

The results of this experiment established the feasibility of PAFC forthe in vivo monitoring of individual cells in the circulatory systems ofliving organisms. Using appropriate contrast enhancement substances, thelaser fluence required for effective detection of cells in circulationwas well below the threshold levels for laser-induced cell damage.

Example 5 Prototype In Vivo Photoacoustic Flow Cytometry System Used toDetect E. coli Bacteria Circulating in Mice

To demonstrate the ability of the prototype photoacoustic flow cytometry(PAFC) system to detect bacteria cells in vivo under biologicalconditions, the following experiment was conducted. The prototype PAFCsystem, previously described in Example 2, was used to detect thebacteria E. coli strain K12, in the circulation of nude mice.

The mouse ear model described in Example 2 was used for all measurementsof circulating bacteria in the experiments described below. Because theendogenous light absorption of E. coli bacteria was relatively weakcompared to the absorption of other blood components in the NIR spectralrange, the bacteria were labeled with NIR-absorbing carbon nanotubes(CNT).

E. coli K12 strain was obtained from the American Type CultureCollection (Rockville, Md.) and maintained in Luria-Bertani (LB) medium,a solution consisting of 1% tryptone, 0.5% yeast extract, and 0.5% NaClat a pH of 7. A 100-μl aliquot of E. coli in PBS was incubated with 100μl of the CNT solution as described in Example 4 for 60 min at roomtemperature.

100-μl suspensions of CNT-labeled E. coli bacteria at a concentration of5×10⁵ cells/ml were injected into the mouse's tail vein, and theclearance of the labeled bacteria was monitored using PAFC measurementstaken from 50-μm diameter microvessels in the ears of mice. Laser energywas delivered at a wavelength of 850 nm, a beam diameter ofapproximately 50 μm and at a laser fluence of 100 mJ/cm². PAFCmeasurements, summarized in FIG. 8, detected a rapid appearance of thebacteria in circulation after injection, and the bacterialconcentrations in the blood decreased exponentially over the next 15-17minutes.

The results of this experiment confirmed the feasibility of PAFC for thein vivo monitoring of individual cells in the circulatory systems ofliving organisms. The laser fluence required for effective detection ofE. coli cells in circulation was well below threshold levels forlaser-induced cell damage.

Example 6 In Vivo PAFC Used to Detect Circulating Exogenous MelanomaCells

To demonstrate the ability to use in vivo PAFC to detect unlabeledmelanoma cells in circulation with extremely high sensitivity throughskin cells with varying levels of melanin pigmentation, the followingexperiment was conducted.

B16F10 cultured mouse melanoma cells (ATCC, Rockville, Md.) were used inthis experiment. The cells were maintained using standard procedures(Ara et al. 1990, Weight et al. 2006, Zharov et al. 2006), includingserial passage in phenol-free RPMI 1640 medium (Invitrogen, Carlsbad,Calif.) supplemented with 10% fetal bovine serum (FBS, Invitrogen). Forcomparison to the detection of unlabelled melanoma cells, the endogenouscell absorption was increased by staining with ICG (Akorn Inc., USA), astrongly absorbent dye in the NIR range, for 30 min at 37° C. and in thepresence of 5% CO₂. No toxicity was observed after labeling as assessedusing the trypan blue exclusion assay (data not shown).

In vivo measurements of melanoma cells used the PAFC system previouslydescribed in Example 2 with a laser wavelength of 850 nm and a laserfluence of 80 mJ/cm². This wavelength falls within a region in which theabsorbance of melanoma cells is relatively high compared to theabsorbance of hemoglobin, a major component of blood, as determined byin vitro measurements summarized in FIG. 9.

To estimate the influence of endogenous skin melanin on PAFC detectionlimits, Harlan Sprague mice, strain: NIH-BG-NU-XID were used in thisexperiment. Female mice of this strain possess high levels skinpigmentation between 8 and 10 weeks of age. Mice were anaesthetized andplaced on the heated microscope stage as previously described in Example2.

A 200-μl volume of saline solution containing approximately 10⁵ mousemelanoma cells was injected into the mouse circulatory system through atail vein and then monitored using the PAFC system. The number ofmelanoma cells per minute detected using PAFC for melanoma cells afterinjection are summarized in FIG. 10 for melanoma cells with low melanincontent (FIG. 10A) and for melanoma cells with high melanin content(FIG. 10B). In the first 5 minutes of PA detection following intravenousinjection of cultured mouse melanoma cells, 600±120 PA signals(representing melanoma cells) per hour were observed, and the rate ofdetection of melanoma cells steadily decreased over the subsequent 20-30min. Approximately 20 cells/hour and 4 cells/hour were detected after 24h and 48 h of monitoring, respectively. The initial PA signal rate afterthe injection of melanoma cells stained with ICG contrast enhancementsubstances was 720±105 cells/hour (data not shown). Assuming that allstained melanoma cells were detected by in vivo PAFC, 82.4% of theunlabelled melanoma cells in circulation were detected by in vivo PAFCmeasurements.

The results of this experiment demonstrated the ability of in vivo PAFCto detect and monitor the appearance and progression of metastaticmelanoma cells in circulation non-invasively.

Example 7 In Vivo PAFC was Used to Detect Circulating SpontaneousMetastatic Cells During Tumor Progression

An experiment was conducted to determine the ability of in vivo PAFC todetect relatively scarce endogenous metastatic melanoma cellscirculating in lymph vessels. The PAFC system described in Example 2 wasused to monitor endogenous metastatic melanoma cells in mice. The lasercharacteristics used in this experiment are identical to those describedin Example 5.

Nude mice were anaesthetized and placed on the heated microscope stageas previously described in Example 2. The ear blood vessels underexamination were located 50-100 μm deep and had diameters of 35-50 μmwith blood velocities of 3-7 mm/sec. To increase the probability ofdetection of rare metastatic cells, blood vessels with relatively largediameters of 150-300 μm and flow velocities up to 10-30 mm/s in the skinof the abdominal wall were examined using a customized skin foldchamber.

50-μl suspensions containing 10⁶ B16F10 cultured mouse melanoma cells(ATCC, Rockville, Md.) were subcutaneously injected into nude mice.Melanoma tumors subsequently formed in the ears of the mice and in theskin on the backs of the mice. PAFC was performed on ear and abdominalblood vessels to monitor the circulatory system for the appearance ofmetastatic cells, and PA mapping, described below, was used to monitorthe growth of tumors.

During ear tumor development, individual or groups of melanoma cellswere first detected in the skin area close to the tumor site on thesixth day following tumor inoculation using PA mapping measurements. PAmapping measurements utilized PA signals derived by scanning a focusedlaser beam with diameter of 10 μm across ear. Metastatic cells firstappeared in ear microvessels near the tumor on the twentieth day afterinoculation at a rate of 12±5 cells/hour (data not shown). Surprisingly,during the same time period, no melanoma cells had yet been detected inthe abdominal skin blood vessels. 25 days after inoculation, the averagecount of melanoma cells detected in the ear veins increased to 55±15cells/hour, and at this same time, melanoma cells were detected inabdominal wall skin vessels at a rate of 120±32 cells/hour. Thirty daysafter inoculation, the detection rate decreased to 30±10 cells/hour inthe abdominal vessel, which may be attributed to inhibition ofmetastatic cell production in the primary tumor. PA mapping of selectedtissue and organs revealed multiple micrometastases in cervical andmesenteric lymph nodes, as well as in lung and liver tissues.

PAFC measurements of the nude mouse back tumor model revealed theappearance of metastatic melanoma in abdominal skin blood vessels closeto the tumor site on day 5, much earlier than in the tumor ear model.This indicates a much greater likelihood of detecting the initialmetastatic process in the vicinity of the primary tumor.

Thirty days after tumor inoculation, the average concentration ofmelanoma cells was 150±39 cells/ml, corresponding to a circulating rateof approximately 4-10 cells/min in a 50-mm blood vessel and a flowvelocity of 5 mm/s. The ultimate PAFC threshold sensitivity of the nudemouse back tumor model was estimated as 1 cell/ml. This circulating ratecorresponded to an incidence of approximately one melanoma cell among100 million normal blood cells.

The results of this experiment indicated that in vivo PAFC and PAmapping were sensitive methods with which to monitor the development ofmetastasized melanoma cells non-invasively, with high sensitivity andaccuracy.

Example 8 In Vivo PAFC was Used to Detect Spontaneous Metastatic Cellsin Lymphatic Vessels During Tumor Progression

To determine the feasibility of detecting individual metastatic cells inlymph flow, the following experiment was conducted. A photoacoustic flowcytometer (PAFC) was used to monitor lymph flow for the presence of WBC,RBC, and metastatic melanoma cells.

The animal models used in this experiment were nu/nu nude mice, weighing20-25 g (Harlan Sprague-Dawley). PAFC measurements were taken using thelymphatic vessels in the ears using a heated platform as described inExample 2. Melanoma tumors in the ear and back skin of the mice wereinduced by the subcutaneous injection of B16F10 mouse melanoma cells asdescribed in Example 6.

To locate the lymphatic vessels in the mouse ear, a PA mapping processusing a PA contrast agent was used. Ethylene blue (EB) dye, commonlyused for lymphatic research, was injected into the lymphatic vesselwalls. A 639 nm laser beam was then used to illuminate the lymphaticvessel at a wavelength of 639 nm, corresponding to the maximumabsorption of EB dye, and the resulting PA signal emitted by the EB dyewas monitored. The position of the laser beam on a lymph vessel wasfixed when the PA signal amplitude reached its maximum at the laserwavelength of 639 nm.

In vivo PAFC detection of unlabeled melanoma cells relied on melanin asan intrinsic cell marker, as in Example 7. Melanoma cells were detectedusing a laser wavelength of 850 nm, a laser fluence of 35 mJ/cm², and alaser beam diameter of approximately 50 μm. In mice with induced skinmelanomas, metastatic cells were observed to appear in a lymphaticvessel of the mouse's ear on the fifth day after inoculation at a rateof 1.2±0.5 cells/min, which steadily increased over the course of 2weeks (data not shown). In mice with a melanoma tumor in the ear,melanoma cells appeared in skin lymphatics 20 days after inoculation. 30days after inoculation strong PA signals detected the presence ofmetastatic melanoma cells in the sentinel lymph nodes, which was laterconfirmed by histology (data not shown). FIG. 11 shows the PA signalsdetected from single metastatic melanocytes circulating in the lymphaticvessel in the mouse ear five days after tumor inoculation.

The results of this experiment demonstrated the feasibility of detectingrelatively scarce metastatic melanoma cells circulating in the lymphaticsystem using in vivo PAFC techniques, with high sensitivity andaccuracy.

Example 9 In Vivo PAFC was Used to Detect Red Blood Cells andLymphocytes Simultaneously Circulating in Lymph Vessels

To determine the feasibility of detecting unlabeled individual cells ofdifferent types circulating in lymph flow, the following experiment wasconducted. A photoacoustic flow cytometer (PAFC) was used to monitorlymph flow for the presence of red blood cells and lymphocytes.

The animal models used in this experiment were 150-200 g rats (HarlanSprague-Dawley). PAFC measurements were taken using lymphatic vessels inthe mesentery of the rat, using the method described in Example 3.Lymphatic vessels were located, and the laser was focused on thelymphatic vessel using the methods described in Example 8.

Spectroscopic studies in vitro revealed that PA signals from lymphocytesreached maximal amplitude in the visible-spectral range near 550 nm,associated with cytochrome c acting as an intrinsic absorption marker(data not shown). Background PA signals from vessels and surroundingtissues were approximately 4-6-fold less than from single lymphocytes atthis wavelength due to the low level of background absorption and laserfocusing effects.

The in vitro PAFC system described in Example 2 was used to detectcirculating cells in the lymphatic vessels of the rat mesentery. Thelaser used in the PAFC system had a wavelength of 550 nm and a fluenceof 100 mJ/cm², and a circular beam diameter of approximately 50 μm. Thecell detection rate obtained in lymphatic vessels was 60±12 cells/min. Agraph showing the PA signals detected by the PAFC system in a ratmesentery lymphatic vessel is shown in FIG. 12. Lymphocyte heterogeneityresulted in 2-2.5-fold fluctuations in PA signal amplitude from cell tocell. A small fraction of the detected cells had strong PA signalamplitudes exceeding those of the lymphocyte signals by a factor of 10to 20-fold. One such strong PA signal is shown as a white bar in FIG. 12at 28 seconds. Subsequent spectral and imaging analysis identified raresingle red blood cells (RBCs) as the sources of these excessively strongPA signals.

The results of this experiment demonstrated that the in vivo PAFC systempossessed sufficient sensitivity and accuracy for the simultaneousdetection of red blood cells and lymphocytes circulating in thelymphatic vesicles.

Example 10 In Vivo Two-Wavelength PAFC was Used to Discriminate Between3 Different Exogenously Labeled Cell Types in Circulation within LymphVessels

To demonstrate the ability of the photoacoustic flow cytometry (PAFC)system to detect cells using more than one wavelength of laser light,the following experiment was conducted. In this experiment, a PAFCsystem was used to detect exogenous blood cells that were labeled withthree different nanoparticles, while circulating in blood vessels (datanot shown) and in lymphatic vessels. The PAFC system detected the cellsby illuminating the cells with laser pulses of two different wavelengthsin the near-infrared (NIR) spectrum.

A PAFC system similar to that described in Example 2 was used to detectthe circulating cells. However, in the PAFC system used in thisexperiment, the laser of the PAFC system pulsed light at two differentwavelengths, corresponding to the wavelengths of maximum absorption fortwo of the nanoparticles used to label the cells. The first laser pulsewas at a wavelength of 865 nm, a laser fluence of 35 mJ/cm², and pulseduration of 8 ns. 10 s after the end of the first laser pulse, a secondlaser pulse was delivered at a wavelength of 639 nm, a laser fluence of25 mJ/cm², and pulse duration of 12 ns. The paired laser pulses wererepeated at a frequency of 10 Hz.

The animal models used in this experiment were nu/nu nude mice, weighing20-25 g (Harlan Sprague-Dawley). PAFC measurements were taken usinglymphatic vessels in the mesentery of the mouse, using the methodsdescribed in Example 3. Lymphatic vessels were located, and the laserwas focused on the lymphatic vessel using the methods described inExample 8.

Normal fresh blood cells were obtained from heparinized whole-bloodsamples of donor mice after terminal blood collection. Red blood cellswere isolated by simple centrifugation, and lymphocytes were isolated byHistopaque (Sigma-Aldrich) density gradient centrifugation asrecommended by the supplier.

The nanoparticles used to label the various blood cells used in thisexperiment were gold nanorods (GNR) and gold nanoshells (GNS), providedby The Laboratory of Nanoscale Biosensors at the Institute ofBiochemistry and Physiology of Plants and Microorganisms in Saratov,Russia. The GNR had an average diameter of 16 nm, an average length of40 nm, and a relatively narrow absorption band of 660±50 nm. The GNS hadan average diameter of 100 nm, and a maximum absorption near 860 nm.Both GNR and GNS were coated with polyethylene glycol in the processdescribed in Example 3. Single-walled CNT with an average length of 186nm and an average diameter of 1.7 nm were purchased from CarbonNanotechnologies Inc. CNT absorb laser energy over a wide range ofwavelengths with an efficiency that monotonically decreases aswavelength increases. All particles were in suspension at aconcentration of about 10¹⁰ nanoparticles/ml.

Live neutrophils were labeled with the GNS, live necrotic lymphocyteswere labeled with the GNR and apoptotic lymphocytes were labeled withthe CNT. The cells were labeled by incubating 100-μl aliquots of eachcell type in phosphate-buffered saline with 100 μl of CNT, GNR, or GNSfor 15 min at room temperature.

The labeled cells, mixed in approximately equal proportions, wereintravenously injected into the tail vein of the mouse. After 6 h,mesenteric lymphatics were illuminated with two laser pulses atwavelengths of 865 nm and 639 nm as described above. PA signals at arate of 1-3 signals/min were detected at this time.

The PA signals had one of three distinctive temporal shapes associatedwith the response of the three different labels to the paired laserpulses, shown in FIG. 13. PA signals from necrotic lymphocytes markedwith GNR were generated in response to the 639 nm laser pulse only,after a 10-μs delay, as shown in FIG. 13A. The apoptotic lymphocytesmarked with GNS generated PA signals in response to laser pulse at awavelength of 865 nm with no delay, as shown in FIG. 13B. Liveneutrophils marked with CNT generated two PA signals after a 10-μsdelay, as shown in FIG. 13C. One signal was generated in response to the639 nm laser pulse, and the second PA signal was generated in responseto the 850-nm laser pulse, due to comparable CNT absorption at bothwavelengths.

The results of this experiment demonstrated that with the use of variouscontrast substances and two wavelength cell identification techniques,the in vivo PAFC apparatus detected and discriminated between liveneutrophils, necrotic lymphocytes, and apoptotic lymphocytes that werecirculating in the lymphatic vessels. This method may also be extendedto unlabelled cells circulating in the lymphatic or circulatory systems,using a pair of laser pulse wavelengths selected to generate a unique PAsignal shape for each cell type to be detected.

Example 11 Spatial Resolution and Maximum Detectible Vessel Depth of aPrototype In Vivo PAFC System was Assessed

To determine the maximum spatial resolution and maximum detectiblevessel depth of the PAFC system, the following experiment was conductedusing the prototype PAFC system described in Experiment 2 and the mouseear model with circulating melanoma cells, as described in Example 7.Mouse melanoma cells were injected into the tail veins of nude mice andPAFC measurements were conducted as described in Example 7.

The PAFC system achieved a lateral resolution of 5-15 μm when detectingmelanoma cells circulating in mouse ear blood vessels with diameters of10-70 μm at depths of 50-150 μm. However, when melanoma cellscirculating in mouse ear blood vessels at a depth of 0.5 mm weremeasured, the lateral resolution decreased to 30-50 μm due to thescattering of the 850 nm laser pulses by the additional tissue betweenthe PAFC laser and the targeted blood vessels.

The maximum potential of the PAFC to detect cells circulating in deepvessels was estimated by overlaying layers of mouse skin of varyingthickness over intact mouse skin containing peripheral blood vessels ata depth of approximately 0.3 mm below the surface of the intact skin.Using the PAFC system described in Example 2 with an unfocusedultrasound transducer (Panametrics model XMS-310, 10-MHz), PA signalswere detected at total skin thicknesses up to approximately 4 mm, with a27-fold signal attenuation due to light scattering. When a focusedultrasound transducer was used (Panametrics model V316-SM, 20 MHz, focallength 12.5 mm), PA signals were detected from melanoma cellscirculating in the mouse aorta at a depth of approximately 2.5 mm,resulting from a laser pulse wavelength of 850 nm. Even at a totaltissue depth as high as 11 mm, the PA signals emitted by circulatingmetastatic melanoma cells illuminated by 532 nm laser pulses remaineddiscernible from the background PA signals from surrounding tissues. Thelateral resolution at this vessel depth, measured by changing the angleof the ultrasonic transducer, was estimated to be approximately 250 μm(data not shown).

The results of this experiment demonstrated that the PAFC system wascapable of detecting circulating melanoma cells at a vessel depth of upto 11 mm with a resolution of approximately 250 μm. This resolution maybe improved significantly through the use of higher frequency ultrasoundtransducers, such as 50 MHz transducers.

Example 12 The Sensitivity of the Spatial Resolution of a Prototype InVivo PAFC Device to Skin Pigmentation Levels was Assessed Using the NudeMouse Model

To determine the sensitivity of the PAFC system to the level of skinpigmentation, the following experiment was conducted. The PAFC devicedescribed in Example 2 was used to measure PA signals from blood vesselsin nude mice skin with low and high levels of pigmentation using methodssimilar to those described in Example 7.

In the low-pigmented nude mouse model, the background PA signal fromskin cells was very weak. PA signals measured by a high frequencyultrasound transducer (Panametrics model V-316-SM, 20 MHz) resultingfrom the simultaneous irradiation of two circulatory vessels at depthsof approximately of 0.3 mm and 2.4 mm, were determined to have a timeseparation of approximately 1.4 ms. This delay is consistent withsignals emitted by cells with a separation distance of 2.1 mm, assuminga velocity of sound in soft tissue of approximately 1.5 mm/ms. Similarresults were obtained for measurements of circulatory vessels in thehighly pigmented nude mouse model (data not shown).

The results of this experiment demonstrated that the level of skinpigmentation did not significantly affect the spatial resolution of thePAFC device. For strongly pigmented skin, the assessment of deepervessels may actually be enhanced because the skin pigmentation mayfacilitate the discrimination between PA signals from circulatingindividual cells and PA signals from the skin.

Example 13 Methods of Enriching the Incidence of Circulating MetastaticCells Measured by PAFC In Vivo were Demonstrated Using the Mouse EarModel

To determine the feasibility of novel methods for increasing theconcentrations of circulating metastatic cells detected by the in vivoPAFC device, the following experiment was conducted. Using the mouse earmodel to measure the incidence of circulating metastatic melanoma cells,as described in Example 7, the effect of gentle mechanical squeezing ofblood microvessels was assessed. This method of enriching the localincidence of rare circulating cancer cells in vivo exploited the sizedifferences between melanoma cells (16-20 mm), WBC (7-8 mm), and RBC(5-6 mm) and the high deformability of RBC compared to cancer cells. Thelumen size of the microvessel was decreased to 10-15 m through gentlemechanical squeezing of blood microvessels in 50-m microvessels of mouseear. After squeezing a 50-m mouse ear blood vessel for 10 min, thenquickly releasing the vessel, the rate of metastatic melanoma cellsmeasured by PAFC immediately after vessel release increasedapproximately 8-fold, relative to the rate measured before squeezing.The degree of blood vessel squeezing could be controlled by monitoringincreases and decreases in PA signal amplitudes.

The results of this experiment demonstrated that local enrichment ofcirculating metastatic melanoma cells was achieved through themechanical restriction of circulatory vessels.

Example 14 The Background Absorption by Surrounding Blood Cells wasManipulated by Changes in Blood Oxygenation, Hematocrit, and BloodOsmolarity

To determine the effects of changes in blood oxygenation, hematocrit,and osmolarity on the background absorption of blood cells during invivo PAFC, the following experiment was conducted. The absorption oflaser energy by hemoglobin in its oxygenated (HbO₂) and deoxygenated(Hb) forms differs, depending on the oxygen saturation state of thehemoglobin and the wavelength of the laser pulse. The total absorptionof red blood cells decreases as oxygenation increases for laser pulsewavelengths 810-900 nm, and the absorption of red blood cells decreaseswith increasing blood oxygenation at laser pulse wavelengths of 650-780nm. Thus, the oxygenation of the red blood cells can be manipulated tominimize the background PA signals emitted by the red blood cells.

Pure oxygen was delivered to a mouse using a mask around the mouse'shead, and the background PA signal obtained before and after theincreased blood oxygenation was measured using the in vivo PAFC systemdescribed in Example 2. The increased blood oxygenation resulting fromthe exposure of the mouse to pure oxygen for 15 minutes caused thebackground PA signal from veins to decrease by a factor of 1.36±0.14,using a laser pulse wavelength of 750 nm. Replacing the delivery of pureoxygen with the delivery of pure nitrogen led to a 35% decrease inbackground PA signal in an arteriole at a laser pulse rate of 900 nm.

Another experiment was conducted to assess the effects of decreasing thedensity of the circulating RBC as measured by the hemotocrit on thebackground signal from circulating red blood cells. The hemotocrit of amouse's blood was temporarily reduced by the intravenous injection of0.5 ml of standard saline solution into the vein tail. After the salineinjection, PA signals from a 50-μm ear mouse vein dropped by a factor of2.3±0.3, and nearly returned to initial levels within about 1.5 minutes.

Blood osmolarity causes an increase in the RBC volume (swelling) thatresulted in a decrease in the average intracellular Hb concentration.Injection of 100-mL of hypertonic NaCl solution into the mouse tail veinled to an approximately 2-fold decrease in the PA signal in the earvein.

The results of this experiment demonstrated that the background PAsignals resulting from the emission of PA signals by red blood cells maybe minimized by manipulation of the chemical environment of the blood,including blood oxygenation, hemotocrit, and blood osmolarity. Theseapproaches may be readily applicable to human subjects because theprocedures used in this experiment are routinely used in clinicalpractice.

Example 15 Microbubbles Conjugated with Nanoparticles were Assessed as aContrast Agent for PAFC

To assess the effectiveness of microbubbles conjugated withnanoparticles as a contrast agent in PAFC, the following experiment wasconducted. Microbubbles (Definity Inc.) with average diameters of 2-4 mwere incubated with PEG-coated gold nanoshells (GNS), previouslydescribed in Example 10 for 1 hr at room temperature. The measurement ofPA signals in vitro, as described in Example 1 was conducted formicrobubbles only, GNS only and microbubbles conjugated with GNS. Themicrobubbles conjugated with GNS emitted the strongest PA signals, theGNS only emitted somewhat weaker PA signals, and the microbubbles aloneemitted negligible PA signals (data not shown).

Increasing the energy of the laser pulses illuminating theGNS-conjugated microspheres led to a dramatic increase of the emitted PAsignals, followed by the disappearance of the microbubbles after asingle laser pulse. This observation was attributed to the laser-inducedoverheating of the GNS leading to a dramatic temperature increase of thegas trapped inside of the microbubbles that ultimately ruptured themicrobubbles.

The results of this experiment demonstrated that microbubbles conjugatedwith GNS were an effective contrast agent, but that the energy of thelaser pulses must be carefully moderated to avoid bursting themicrobubbles. Because the microbubbles may be selectively attached toblood clots or taken up by activated white blood cells, this contrastagent may expand the potential applications of in vivo PAFC to includethe detection of blood clots and certain activated white blood cells.

Example 16 Two-Wavelength In Vivo PAFC Used to Detect CirculatingExogenous Melanoma Cells

To demonstrate the ability to use two-wavelength in vivo PAFC to detectinjected unlabeled melanoma cells in circulation with extremely highsensitivity, the following experiment was conducted. B16F10 culturedmouse melanoma cells (ATCC, Rockville, Md.) were obtained and maintainedas described in Example 6. The experiments were performed using a nudemouse ear model similar, described in Example 2 (n=25). To mimicmetastatic cells, approximately 10⁵ tumor-derived B16F10 cells in a100-μl volume of saline solution were injected into the mousecirculatory system through a tail vein and then monitored in an ear veinusing an apparatus and methods similar to those described in Example 10.An ear blood vessel was illuminated by two laser pulses at wavelengthsof 865 nm and 639 nm with a 10-ms delay between the pulses.

The melanoma cells were distinguished from surrounding blood cells,based upon the distinctive absorption spectra of the melanoma cells, asdescribed previously in Example 6 and summarized in FIG. 9. Melanomacells emitted two PA signals with a 10-ms delay, corresponding to thetwo laser pulses. The first PA signal, induced by the 639 nm laserpulse, had a higher amplitude than the PA signal induced by the 865 nmpulse, as shown in FIG. 14A. Red blood cells, the most numerous bloodcells in circulation, generated two PA signals with lower amplitudesthan the corresponding PA signals generated by the melanoma cells. Inaddition, for the red blood cells, the amplitude of the PA signalinduced by the 865 nm pulse was slightly higher than the PA signalinduced by the 639 nm laser pulse, as shown in FIG. 14B.

The PA signals corresponding to the melanin particles were cleared overa two-hour period following the injection, as shown in FIG. 15.

Based on comparisons to similar data measured for melanoma cells labeledwith markers that emitted strong PA signals, it was estimated thatapproximately 89% of the unlabelled melanoma cells were detected (datanot shown). This percentage was lower than that found in previous invitro studies (96%) and indicated a false-negative-signal rate of 1.5cells/min because of the influence of background absorption by RBCs(data not shown). Longer-term monitoring of PA signals from ear bloodvessels without prior melanoma cell injection detected no false-positivesignals using as its criteria a signal-to-noise ratio≧2, where thesignal noise was associated with fluctuations of laser energy and thedensity of red blood cells in the detected volume.

The results of this experiment demonstrated that two-color in vivo flowcytometry was an effective method of detecting metastatic melanoma cellsin circulation. It was estimated that the method described abovedetected approximately 89% of the melanoma cells in circulation, withslightly lower detection rates due to skin pigmentation.

Example 17 Two-Wavelength In Vivo PAFC was Used to Detect CirculatingSpontaneous Metastatic Cells During Tumor Progression

An experiment was conducted to determine the ability of two-wavelengthin vivo PAFC to detect relatively scarce endogenous metastatic melanomacells circulating in lymph vessels. The PAFC system described in Example10 was used to monitor endogenous metastatic melanoma cells in mice.Tumors were induced in nude mice by subcutaneous injections of melanomacells using methods similar to those described in Example 7. Tumorsformed and proliferated in the skin of the ear and the back of the nudemice over a period of 4 weeks, as previously described in Example 7.

PAFC was used to count spontaneous metastatic melanoma cells in a ˜50μm-diameter ear blood vessel and a 100-200-μm-diameter skin blood vesselduring tumor progression in the ear and skin of a mouse, as summarizedin FIG. 16. As previously described in Example 7, the skin tumor growthrate was faster than that of the ear tumors, and metastatic melanomacells appeared more quickly in the circulation, as indicated by the meancell detection rate measured in the skin capillaries, shown as solidsquare symbols in FIG. 16. In particular, within the first week afterthe induction of the tumors, about 1-4 melanoma cells/min were detectedin the skin vasculature, and as the tumor size increased, the rate ofdetection of metastatic melanoma cells gradually increased to about 7cells/min and about 12 cells/min after 3 weeks and 4 weeks,respectively.

The results of this experiment indicated that in vivo PAFC and PAmapping were sensitive methods with which to monitor the development ofmetastasized melanoma cells non-invasively, with high sensitivity andaccuracy.

Example 18 PAFC System was Used to Determine Photoacoustic Response ofQuantum Dot Markers In Vitro

An experiment was conducted to determine the ability of two-wavelengthin vivo PAFC to detect quantum dot cell markers in vitro. The PAFCsystem described in Example 2 was used to measure photoacoustic pulsesemitted by quantum dots in response to laser pulses with wavelengths of625 nm, pulse widths of 8 ns, and laser fluences ranging 0.001-10 J/m².The laser beam used to pulse the quantum dots had a diameter of about20-30 μm in the sample plane. Quantum dots were obtained commerciallywith a polymer coating as well as with a streptavidin protein coating(Qdot 655 nanocrystals, Invitrogen, Carlsbad Calif.). The quantum dotshad diameters of about 15-20 nm and an emission wavelength of about 655nm. Either single or aggregations of quantum dots were diluted with abuffer of 2% BSA/PBS and mounted in a layer of less than 1 μm on amicroscope slide.

The PAFC system was used to pulse the quantum dot preparation with laserfluences ranging from 0.001-30 J/m². The magnitudes of the PA signalsemitted by the quantum dots are summarized in FIG. 17. The PA signalresponse of the quantum dot preparations had a non-linear response tothe variations in laser fluences. PA signal amplitude graduallyincreased in the laser fluence range from 0.1-1 J/cm². Through the laserfluence range between 1.5-7 J/cm², the response increased dramaticallyin a non-linear manner, and continued to increase in magnitude up to alaser fluence of 15 J/cm². At laser fluences above 15 J/m², theresponses of the quantum dot preparations were saturated.

The PA signal response as a function of the number of laser pulses forlaser fluences of 1.2, 4.0, 6.2, and 12.4 J/cm² are summarized in FIG.18. There was no sign of alteration of the laser pulse-induced PAsignals at laser fluences below 3 J/cm², indicating no blinkingbehavior, unlike the stereotypical fluorescent blinking behaviorobserved in quantum dots. At higher laser fluences, significantdecreases in the PA signal amplitude were observed with an increase inthe number of pulses, possibly due to laser induced melting ofthermal-based destruction by explosion of the quantum dots.

The results of this experiment indicated the quantum dots generatedstrong PA signals in response to laser pulses.

Example 19 PAFC System was Used to Detect Bacteria and Melanoma CellsMarked with Magnetic Nanoparticles In Vivo

To demonstrate the application of magnetic nanoparticles asphotoacoustic (PA) contrast agents, the following experiment wasconducted.

S. aureus bacteria, described in Example 4, and melanoma cells,described in Example 6, were labeled with super paramagnetic iron oxidenanoparticles (Clementer Associates, Madison, Conn.). The nanoparticlesconsisted of a 50-nm core of magnetite (Fe₃O₄), coated with a 10-15 nmlayer of Dextran and fluorescent dye. Both bacterial cells and melanomacells were cultured at a density of approximately 10⁶ cells/mL, andmagnetic nanoparticles were added to the cell cultures at a density of0.5 mg/mL, and loaded into the cells by endocytosis for a minimum of 1hour at 37° C. Labeled cells were centrifuged at 5,000 rpm for 3 minutesand the resulting pellet was resuspended in PBS.

The photoacoustic flow cytometry system (PAFC) system was similar indesign to the PAFC system previously described in Example 2, withmodifications to the laser, amplifier, and transducer components. Adiode laser 905-FD1S3J08S (Frankfurt Laser Company) with driver (IL30C,Power Technology Inc, Little Rock, Ark.) was used to pulse the unboundmagnetic nanoparticles and labeled cells with a pulse width of 15 ns,and a pulse repetition rate of 10 kHz. The laser beam dimensions used topulse the nanoparticles and cells had an elliptical cross-section withminor and major axis dimensions of 11 μm and 75 μm, respectively, and afluence energy maximum of 0.6 J/cm². The laser-induced PA signals weredetected by a 5.5 mm-diameter, 3.5 MHz ultrasound transducer (model6528101, Imasonic Inc., Besançon, France), amplified using a 2 MHzamplifier (Panametrics model 5660B) and recorded with a Boxcar datarecorder (Stanford Research Systems, Inc.) and a Tektronix TDS 3032Boscilloscope.

To determine the clearance rate of unbound magnetic nanoparticles, thenude mouse ear model described in Example 2 was used. A 100-mL PBSsuspension of the magnetic nanoparticles at a concentration of about10¹¹ nanoparticles/mL was injected into the vein tail of the mice.

The magnetic nanoparticles were detected using the PAFC system describedabove. The laser pulses were delivered to the unbound magneticnanoparticles at a wavelength of 639 nm and a laser fluence of 1.5J/cm². The detection and subsequent clearance of the magnetic particlesin the nude mouse ear model are summarized in FIG. 19. PA signalscorresponding to the magnetic nanoparticles appeared within the firstminute after injection. The PA signals were a combination of afluctuating continuous PA background with superimposed large-amplitudePA signals. The magnitude of the background signal associated with themagnetic nanoparticles exceeded the PA background signals from the bloodvessels by a factor of 2-3. The stronger but less frequentlarge-amplitude PA signals may be associated with random fluctuations ofthe number of magnetic nanoparticles in the detected volume andappearance of small aggregates of magnetic nanoparticles. The clearancetime of the magnetic nanoparticles from the mouse ear microcirculationwas in the range of 10-20 minutes.

Approximately 10⁵ B16F10 melanoma cells or S. aureus labeled withmagnetic nanoparticles in 100 μL of saline solution were injected into amouse tail vein and then monitored in the mouse ear using the PAFCsystem described above. Labeled melanoma cells were detected using a 905nm, 0.4 J/cm² laser pulse, and the bacterial cells were detected usingan 850 nm, 0.9 J/cm² laser pulse. The resulting PA signals emitted by S.aureus and melanoma cells labeled with magnetic nanoparticles aresummarized in FIG. 20. Numerous PA signals from individual circulatingcells were detected, with a maximum rate of detection within the first1-3 minutes. The average half-life of the labeled bacteria and cancercells in the blood microcirculation was 4.5 and 12 min, respectively.

After the labeled melanoma cells and bacteria were essentially clearedfrom the circulation and only rare PA signals were detected, a localpermanent magnetic field was imposed through intermediate tissue to theblood microvessels. The local permanent magnetic field was provided by acylindrical Neodymium-Iron-Boron (NdFeB) magnet with Ni—Cu—Ni coatingthat was 3.2 mm in diameter and 9.5 mm long with a surface fieldstrength of 0.39 Tesla (MAGCRAFT, Vienna, Va.). The distance between themagnet and the microvessel walls ranged between 50-100 μm. As shown inFIGS. 21 and 22, the application of the magnetic field to the bloodmicrovessels led to an immediate increase in both PA signal amplitudesand rate of detection in the vicinity of the magnet for the labeledmelanoma cells and bacterial cells respectively.

The results of this experiment demonstrated that magnetic nanoparticlescould be used to label circulating melanoma and bacteria cells for usein the prototype PAFC system. Further, a magnetic field applied to theblood microvessel in which the PAFC detected circulating cells was ableto locally enrich the concentration of cells to be detected.

Example 20 Magnet-Induced Amplification of Signals from CD44+ CellsTargeted by Magnetic Nanoparticles

To assess the viability of manipulating cells labeled with magneticnanoparticles (MNPs) using an external magnetic field, the followingexperiments were conducted.

Human breast cancer cells (MDA-MB-231, American Type Culture Collection,Manassas, Va.) were cultured according to the vendor's specifications.The cells were cultured to confluency in vitro, detached with 0.25%trypsin-0.53 mM EDTA, washed and resuspended in PBS. The resuspendedcells were then incubated for one hour at 37° C. with 30 nm sphericalmagnetic nanoparticles (Ocean NanoTech, Springdale, Ark.) conjugatedwith antibodies targeted to human CD44 receptor (MNP-CD44). In addition,the antibodies were stained with fluorescent labels (fluoresceinisothiocyanate-dextran [FITD], BD Pharmaceuticals) according to themanufacturer's specification prior to conjugation to the MNPs. Theconcentration of MNP-CD44 particles added to the PBS was about0.1×10³-1×10³ particles per suspended cell. The labeled cells wereresuspended in PBS, placed in 8.6 ml wells (Molecular Probes) andcovered with a top cover. In this example, the cells were triplelabeled, since the MNP portion of the MNP-CD44 particle functions as aphotoacoustic and photothermal contrast agent, and the FITD staining ofthe antibody functions as a fluorescent label.

A permanent magnetic field was provided by a magnet tip gently attachedto the top cover of the slides for the manipulation of the labeledcells. The magnet was a cylindrical neodymium-iron-boron (NdFeB) magnetwith Ni—Cu—Ni coating (MAGCRAFT, Vienna, Va.). This cylindrical magnethad a diameter of 3.2 mm, a length of 9.5 mm, and a surface fieldstrength of 0.39 Tesla.

To assess the effectiveness of the magnet at attracting and clusteringthe MNP-CD44 particles, the magnetic tip was attached the top cover of aslide containing suspended MNP-CD44 particles only in PBS at aconcentration of 10¹¹ particles/mL. The attachment of the magnet tip tothe top cover of the slide induced the migration of the MNPs to theimmediate vicinity of the magnet, resulting in a dark spot visible withthe naked eye. The identity of the MNP-CD44 particles within the darkspot was verified by fluorescent microscopy. FIG. 23 shows thefluorescent image of the slide before (FIG. 23A) and after (FIG. 23B)the application of the magnetic field to the top cover; the clusteredMNP-CD44 particles appear as a bright spot in the lower right corner ofFIG. 23B.

Non-linear photothermal (PT) signals were obtained for the same slidebefore and after the application of the magnetic field, as shown in FIG.24. The laser used in this experiment had a wavelength of 639 nm, a beamdiameter of 15 μm, and a fluence of 50 mJ/cm². The PT signal from theregion with a high local concentration of MNP-CD44 particles after theapplication of the magnetic field (FIG. 24B) was 10-20-fold higher thanthe PT signal obtained prior to the applied magnetic field (FIG. 24A).

Single cancer cells labeled with MNP-CD44 as described above weresimilarly assessed before and after exposure to the external magneticfield. As shown in FIG. 25, the application of the external magneticfield induced an enhancement of the local fluorescence gradient withinthe single isolated cell (FIG. 25B) compared to the relativelyhomogenous spatial fluorescent light distribution prior to exposure tothe external magnetic field (FIG. 25A), suggesting magneticfield-induced clustering of the MNPs within the single cell. Further, asshown in FIG. 26, exposure of the isolated labeled cells to the externalmagnetic field resulted in a 6.6-fold enhancement of the PT signalsobtained from these cells (FIG. 26B) relative to the PT signals obtainedfrom the cells before exposure to the magnetic field (FIG. 26A). Theappearance of locally dense intracellular clusters of MNPs is likely dueto the accumulation of the MNPs under the magnet near cellularstructures such as cell membrane that may have acted as mechanicalobstacles to impede the further movement of the MNPs.

The results of this experiment indicated that the labeling of cellsusing MNPs conjugated with antibodies or other biological compoundstargeted toward particular cell types renders the cells amenable tomanipulation using magnetic fields. Further, the external magnetic fieldinduces the formation of intracellular clusters of MNPs, resulting inthe enhancement of PT signals of the labeled cells.

Example 21 Efficacy of Conjugated Nanoparticles Targeted to CirculatingTumor Cells

To assess the efficacy of the binding of nanoparticles conjugated withtarget compounds directed to receptors specific to circulating tumorcells, the following experiments were conducted. A magnetic nanoparticle(MNP) and a gold nanotube (GNT) were conjugated to known ligands ofcancer cell-specific receptors and assessed to determine the contrast ofthe PA signals produced relative to other blood components, theefficiency of binding to circulating cancer cells, the ability tocapture labeled CTCs and circulating MNPs using an external magneticfield, the clearance dynamics of the nanoparticles in vivo, and theclearance dynamics of CTCs labeled using the nanoparticles.

Because human tumor cells are typically heterogeneous, multiplextargeting and a multicolor detection strategy was utilized to increasethe specificity of the nanoparticles needed to implement the in vivoidentification of circulating tumor cells (CTCs). To this end, the CTCswere labeled with two different labeling particles (magneticnanoparticles and golden carbon nanotubes), which emitted photoacoustic(PA) signals distinguishable from background PA signals from surroundingblood cells and endothelial tissues. The PA detection of the CTCslabeled using the MNPs and CTCs was conducted by exposing the CTCs tolaser pulses at two different wavelengths to enhance the contrast of thePA signal produced by each type of labeling particle.

Using methods similar to those described in Example 20, magneticnanoparticles (MNPs) were conjugated to an amino-terminal fragment (ATF)of the human urokinase plasminogen activator, which serves as specificligand for the urokinase plasminogen activator receptors that are highlyexpressed on many types of cancer cells but are expressed at a low levelin normal blood and endothelial cells. These conjugated MNPs (MNP-ATFs),illustrated schematically in FIG. 27, served as dual magnetic andphotoacoustic contrast agents due to the intrinsic absorption propertiesof the Fe₂O₃ core of the MNPs. In addition, the MNP-ATFs were furtherconjugated with fluorescein (FITC) to provide additional fluorescenceimaging capability in a manner similar to Example 20.

The golden carbon nanotubes (GNTs) were conjugated to folate, whichserves as a ligand for the folate receptors that are expressed in cancercells but absent in normal blood. The GNTs selected had average lengthsof about 98 nm and average diameters of about 12 nm. The folate wasconjugated to the GNTs using electrostatic interactions. The resultingfolate-GNT conjugates were washed three times in the presence of 1%polyethylene glycol (PEG) and conjugated with fluorescein (FITC) toprovide additional fluorescence imaging capability. Thesefolate-conjugated golden carbon nanotubes (GNT-FOLs) are illustratedschematically in FIG. 28.

Two laser wavelengths were selected to perform the photoacoustic sensingof the dually-labeled tumor cells. The first wavelength was selected tobe 639 nm to provide strong photoacoustic contrast of the PA signal fromthe MNPs, and the second wavelength of 900 nm was selected to enhancethe contrast of the PA signal of the GNTs relative to other bloodcomponents. An estimated photoacoustic spectra showing the PA signals ofthe MNPs, the GNTs, and the blood background signals are shown in FIG.29, along with the two wavelengths selected for PA sensing.

The human breast cancer cell line MDA-MB-231, which is positive for boththe urokinase plasminogen activator and the folate receptor, were usedin these experiments. To verify the target specificity of the conjugatedMNP nanoparticles in vitro, the cancer cells were incubated withunconjugated MNP and with conjugated MNP-ATF nanoparticles for two hoursat 37° C. After incubation, the cells were subjected to Prussian Bluestaining, which stained the iron cores of any MNPs attached to thecells. FIG. 30 includes microscope images of a single cancer cellincubated with unconjugated MNPs (FIG. 30A) and with MNP-ATF (FIG. 30B).To verify the target specificity of the conjugated GNTs in vitro, thecancer cells were incubated with GNTs conjugated with fluorescein onlyor with the conjugated GNT-FOL nanoparticles for two hours at 37° C.Fluorescent images of a single cell incubated with thefluoroscein-conjugated GNTs (FIG. 31A) and a single cell incubated withthe GNT-FOL (FIG. 31B) indicated that the GNT-FOL attached specificallyto the cancer cells.

A PAFC system similar to that described in Example 10 was used with thefollowing modifications, illustrated in FIG. 32. A diode laser(905-FD1S3J08S, Frankfurt Laser Company) and associated driver (IL30C,Power Technology) was used to deliver laser pulses at a wavelength of905 nm, a pulsewidth of 15 ns and a pulse repetition rate of 10 kHz. Inaddition, a second co-linear probe pulse from a Raman shifter wasdelivered at a wavelength of 639 nm, a pulse duration of 12 ns and at a10-ms delay relative to the 905 nm pump pulse. The delivery of laserradiation to the area of interest was performed either with microscopeoptics or using a 330-mm fiber with focusing tip.

The laser-induced photoacoustic waves were detected using 3.5 MHzultrasound transducers having a diameter of 4.5 mm (model 6528101,Imasonic). The transducer was gently attached to the external surface ofthe sample containing the labeled cells or nanoparticles to be detectedand warmed water or ultrasound gel was topically applied to the surfaceto enhance the acoustic matching between the transducer and the samples.The detected signal was amplified using a 2 MHz, 60 dB gain amplifier(model 5660B, Panametrics), and the amplified signal was digitized,recorded, and analyzed as described in Example 2.

Also shown in FIG. 32 is a magnet similar to the magnet described inExample 20 that was used to apply an external magnetic field to the areaof interest. In selected experiments, a similar magnet was used thatincorporated a custom-made 0.7-mm hole through which the 330-mm fiberwas threaded to deliver the laser radiation. The magnet was gentlyattached to the surface of the sample containing the nanoparticles orlabeled cells to be detected. In those cases in which the sample was alive mouse, the distances between the magnet and examined vessels rangedfrom 50 to 100 mm (mouse ear) or 0.3 to 0.5 mm (abdominal area).

Samples containing suspensions of either 10¹¹ MNPs/ml of 10-nm MNPs inPBS, or a single MDA-MB-231 cell labeled with the MNPs as describedabove were placed onto 120-mm-thick microscope slides. The PAFC systemdetected PA signals generated using laser fluences ranging from about10⁻² to about 10¹ J/cm², either in the presence or absence of anexternal magnetic field that was applied for 10 minutes prior to PAdetection. As shown in FIG. 33, the PA signals from the MNP-labeledcells were significantly higher than the PA signals from unbound MNPs,particularly at the higher laser fluences and after exposure to themagnetic field for 10 min. This signal amplification may be due tomagnet-induced MNP clustering within the labeled cells and laser-inducedmicrobubbles around the MNP clusters.

MNPs and GNPs were spiked into mouse blood samples at a range ofconcentrations and PA signals of the spiked samples were obtained usinglaser pulses at a laser fluence of 20 mJ/cm² and pulse wavelengths of639 nm and 900 nm for the MNP and GNP samples, respectively. Thephotoacoustic signals measured for the two sample types are summarizedin FIG. 34; the lowest detectable concentrations of nanoparticles abovethe background PA signals from other blood components were determined tobe 35 GNTs and 720 MNPs.

Labeling efficiency of the MDA-MB-231 cells using different combinationsof unconjugated and conjugated nanoparticles was assessed using the PAFCsystem on static cell cultures. The samples to be labeled includedMDA-MB-231 cells suspended in PBS, MDA-MB-231 cells spiked into mouseblood, and unspiked mouse blood with no added MDA-MB-231 cells. Thelabeling particles added to the samples included: 1) unconjugated MNPs,2) unconjugated GNTs, 3) a 20:80 ratio mixture of GNTs and MNPs, 4)conjugated MNP-ATF particles, 5) conjugated GNT-FOL particles, and 6) a20:80 ratio mixture of GNT-FOL and MNP-ATF particles. The samples weretreated with the labeling particles for one hour at 37° C. Table 3summarizes the labeling efficiencies obtained using the PAFC system. Theconjugated nanoparticle mixture cocktail showed the best targetingefficiency (96±2.1%) for the cells on mouse blood under staticconditions.

TABLE 3 Labeling Efficiency of Unconjugated vs. Conjugated NanoparticlesLabeling Efficiency (%) Normal Cells in Mouse Cells in Mouse BloodNanoparticles PBS Blood (control) MNP 5 3 5 GNT 15 8 4 MNP + GNT 18 11 8MNP-ATF 85 71 98 GNT-FOL 89 76 96 MNP-AFT + 98 96 9 GNT-FOL

To assess the ability to capture cancer cells labeled with MNP-AFTparticles using a magnetic field, a PAFC flow simulation system, shownin FIG. 35 was used visualize the capture of the labeled cancer cellsand to measure PA signals generated by labeled cancer cells at differentflow velocities ranging from 0.1-10 cm/s. The PAFC flow simulationsystem included a syringe pump attached to a 180 μm diameter glass tube.The glass tube directed the flow of the sample exiting the syringe pumppast a magnet and laser and into a flask. A microscope objective and anultrasound transducer were also attached to the glass tube in closeproximity to the magnet and laser to obtain microscopic images and PAsignals, respectively. Labeled cancer cells were suspended in PBS eitherwith or without additional MNP-AFT particles and observed as they flowedthrough the glass tube at a range of flow velocities. The PA signalsproduced by the labeled cancer cells and the surrounding suspensionmedium are shown in FIGS. 36A and 36B, respectively. FIG. 37 is a seriesof fluorescent microscopic images taken in the vicinity of the magnet oflabeled cancer cells in PBS at a flow velocity of 0.5 cm/s (FIG. 37A),for labeled cancer cells with additional MNP-AFT particles at flowvelocities of 0.1 cm/s (FIG. 37B) and 5 cm/s (FIG. 37C).

The attached magnet of the PAFC flow simulation system captured theMNP-labeled cancer cells at a broad range of flow velocities (0.1-10cm/s), accompanied by strong PA signals from the area under the magnetis excess of those signals outside the magnet corresponding to rareuncaptured cells and unbound MNPs. Both the additional MNPs and theMNP-labeled cells were captured at a flow velocity of 0.1 cm/s, as shownin FIG. 37B. However, increasing the flow velocity to 5 cm/s removedmost of the free MNPs but the MNP-labeled cell remained captured, asshown in FIG. 37C. FIG. 38 summarizes the capture efficiency of thelabeled cells and the MNPs, defined as the relative number of cells orMNPs captured at different flow velocities as a percentage of thecorresponding number captured at a flow velocity of 0.1 cm/s. Thecapture efficiency of the unbound MNPs falls off rapidly as flowvelocity increases above 0.1 cm/s, while the capture efficiency ismaintained at a level of at least 90% for all but the highest flowvelocities. Because magnetic force is proportional to the density ofmagnetic material within a particular volume, the randomly distributedfree MNPs were more likely to be removed from the magnetic field by flowdrag forces than the labeled cancer cells that contained a higher localMNP concentration or dense MNP clusters.

To determine the depletion kinetics of the nanoparticles in vivo, MNPsand GNTs were separately injected through mouse tail vein of nude mice(nu/nu) and the circulation of the nanoparticles was monitored using themouse ear model described in Example 2. The nanoparticles were injectedin two separate samples consisting of MNPs in 10 mL of PBS at aconcentration of 10⁹ nanoparticles/mL, and GNTs in 10 mL of PBS at aconcentration of 10¹¹ nanoparticles/mL. Photoacoustic monitoring ofvessels in the mouse ear was conducted using laser pulses at 639 and 900nm to detect concentration of the circulating nanoparticles. Assummarized in FIG. 39, the half-life of both nanoparticles incirculation was about 15-20 minutes. At later times, rare flashes of PAsignals appeared, preferentially from the MNPs, which were likelyassociated with random fluctuation of nanoparticle numbers in thedetected volume and the non-specific uptake of the nanoparticles bycirculating blood cells such as macrophages. No photoacoustic signalswere detected from either nanoparticle at a concentration of less than10⁹ nanoparticles/mL, suggesting that the PA signals from unbound ornon-specifically bound nanoparticles fell below the background levelfrom the blood.

The depletion kinetics of simulated circulating tumor cells (CTCs) thatwere labeled in vitro and in vivo were similarly assessed. The in vitrolabeled cancer cells were cultured with a 20:80 ratio mixture of GNT-FOLand MNP-ATF particles and then injected into the tail vein of the nudemice. The in vivo labeled cancer cells were formed by first injectingunlabeled cancer cells into the tail vein of the nude mice, followed byan injection of 10 μL of PBS in which a 20:80 ratio mixture of GNT-FOLand MNP-ATF particles was suspended. The labeled cancer cells weremonitored in an abdominal vessel of the mice using the PAFC with laserpulses of 639 nm and 900 nm transmitted to the vicinity of the abdominalvessel via laser fiber at laser fluences of 80 mJ/cm² and 20 mJ/cm²respectively. FIG. 40 summarizes the results of the PA detection of thein vitro and in vivo labeled CTCs.

After intravenous injection of 10⁵ cancer cells labeled with thenanoparticles in vitro, flashes of photoacoustic signals at both 639 and900 nm with dominant amplitude at 900 nm were observed immediately afterinjection, corresponding to the detection of labeled CTCs. The frequencyof detected PA signals subsequently declined and disappeared 60-90minutes after the initial injection of the in vitro labeled CTCs. Afterthe initial injection of the nanoparticles in the in vivo labeling case,photoacoustic signals at both 639 and 900 nm gradually increased infrequency within 8-10 min to approximately the same detection frequencyobserved from cells labeled in vitro. The subsequent decline indetection frequency of the in vivo labeled CTCs followed a similarpattern of decline as the clearance of the in vitro labeled CTCs.Infrequent PA signals associated with the 900 nm pulse only or the 639nm pulse only were detected, which may be associated with the targetingof infrequently-occurring CTCs that express only one of the selectedbiomarkers targeted by the nanoparticle conjugates. The bloodsurrounding the circulating CTCs produced weak background signals withconsistent and comparable amplitudes at both laser pulse wavelengths,and no PA signals with consistent amplitudes consistently above thebackground signal of the blood was detected other than the CTC detectionsignals, indicating a negligible background signal originating fromunbound circulating nanoparticles.

The results of this experiment indicated that conjugated magneticnanoparticles and gold nanotubes, particularly in combination, may beused to label circulating tumor cells with high specificity andefficiency, rendering the labeled CTCs amenable to in vivo detectionusing photoacoustic detection methods.

Example 22 Magnet-Induced Amplification and Visualization of LabeledCD44+ Circulating Tumor Cells targeted by MNPs

To assess the in vivo detection of circulating tumor cells (CTCs)originating from a primary tumor using the in vivo photoacoustic flowcytometry (PAFC) methods described above in combination with celllabeling using conjugated nanoparticles and magnet-induced signalamplification, the following experiments were conducted.

Tumors were induced in nude mice (nu/nu) by inoculating breast cancerxenografts consisting of 5×10⁶ MDA-MB-231 cells subcutaneously into themice. At 2, 3, and 4 weeks after initial tumor development, a 20:80ratio mixture of conjugated MNPs and CNTs (described previously inExample 21) was injected into the tail vein of the mice. After allowing20 minutes for clearing the majority of unbound injected nanoparticles,photoacoustic detection of the labeled CTCs circulating in an abdominalvessel and in an ear vessel was performed using the PAFC device andmethods described in Example 21. The results of these measurements aresummarized in Table 4.

TABLE 4 Circulating Tumor Cells Detected After Inoculation of Nude MiceWith Cancer Xenografts Rate of CTCs Detected (cells/min) AbdominalEar:Abdominal Week Ear Vessel Vessel CTC Ratio 2 0.9 ± 0.3  6 ± 2.1 0.153 7.2 ± 0.3 26 ± 0.3 0.27 4 15.1 ± 2.7  47 ± 6.4 0.32

As shown in Table 4, the ratio of the CTC detection rate in the mouseear vessel to the CTC detection rate in the abdominal vessels increasedfrom 2 weeks to 4 weeks. The CTC detection rate in the mouse ear vein,summarized in FIG. 41, was roughly correlated with the stage of theprimary tumor progression and vessel sizes. Attaching a magnet similarto the magnet described in Example 21 in the vicinity of the abdominalblood vessel 20 min after the injection of conjugated nanoparticle intothe mice at week 1 of tumor development changed the character of thephotoacoustic signal from infrequent flashes of signals to a continuousincrease of photoacoustic signals, as summarized in FIG. 42. Similarpatterns were observed after 2 to 4 weeks of tumor development. As shownin FIG. 43, the signal amplitude in the abdominal vessels of mice atweek 2 of tumor development increased 88-fold within one hour of theapplication of an external magnetic field. Removal of the magnet led tothe release of the trapped CTCs bound to nanoparticles, resulting in adecrease in the PA signal amplitudes. This partial decrease in PA signalamplitude may be due to the remaining CTCs left adhered to the vesselwall.

The results of this experiment indicated that duplex molecular targetingof CTCs with functionalized nanoparticles followed by CTC capture anddetection using dual magnetic-photoacoustic flow cytometry technologymay be feasible for the detection of CTCs circulating in thebloodstream, in vivo, in real time.

Example 23 Magnetic Manipulation and Detection of Blood Cells Using anExtracorporeal Shunt

To assess the efficacy of in vivo detection of circulating blood cellsin an extracorporeal shunt using the in vivo photoacoustic flowcytometry (PAFC) methods described above, in combination with celllabeling using conjugated nanoparticles and magnet-induced signalamplification, the following experiments were conducted.

An extracorporeal shunt, illustrated in FIG. 52A, was used to label,magnetically manipulate, and detect circulating tumor cells from a whiterat. Catheters were inserted into a large artery and a jugular vein ofthe rat as shown in FIG. 52B. Blood from the rat entered theextracorporeal shunt through the arterial catheter and exited the shuntthrough the jugular catheter. Functionalized magnetic 10-nmnanoparticles were injected into the shunt upstream of the detectionpoint near the magnet and laser and ultrasound transducer. The distancesbetween injection site and detection points may be varied by change oftube length in order to enhance the binding of the functionalizedmagnetic nanoparticles to the circulating tumor cells. The magneticallylabeled in-flow tumor cells were captured by the magnetic field producedby the magnet. Laser irradiation of the detection area near the magnetgenerated photoacoustic signals which were detected with the ultrasoundtransducer attached to the tube. The photoacoustic amplitude signalswere found to be correlated with concentration of the magneticallycaptured circulating tumor cells (not shown).

Conventional transmission imaging in the detection area providedinformation used to control the position of the laser beam, magnet, andultrasound transducer. Using the high speed high resolution imaging modeof the optical system also provided visualization of individual movingcells at the single cell level, as shown in FIG. 53C-FIG. 53E formagnifications of 4×, 20× and 100×, respectively.

The results of this experiment demonstrated that the extracorporealshunt provided photoacoustic continuous monitoring of shunted blood flowin an external tube, and the efficient capture of magnetically labeledabnormal circulating objects (e.g., tumor cells, bacteria, toxin, ordrug) targeted by the magnetic nanoparticles within the extracorporealflow. In addition, the magnetic capture of both magnetically-labeledabnormal objects and unbound magnetic nanoparticles prevented theirfurther introduction into the systematic circulation of the rat.

It should be understood from the foregoing that, while particularembodiments have been illustrated and described, various modificationscan be made thereto without departing from the spirit and scope of theinvention as will be apparent to those skilled in the art. Such changesand modifications are within the scope and teachings of this inventionas defined in the claims appended hereto.

REFERENCES

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What is claimed is:
 1. A device for the manipulation and detection of amagnetic target object within a moving biofluid of a living organism,comprising: an in vivo flow cytometer for detecting the magnetic targetobject within an area of interest; and at least one magnet for producinga magnetic field that manipulates the magnetic target object within thearea of interest wherein the in vivo flow cytometer is an in vivophotoacoustic flow cytometer comprising a laser fiber for delivering atleast one laser pulse to the area of interest, wherein the laser fibercomprises a focusing tip to transmit the at least one laser pulse to thearea of interest; and wherein the at least one magnet comprises amagnetic material forming a channel, wherein the laser fiber passesthrough the channel and the focusing tip is situated at a laser pulselocation that is essentially coincident to a corresponding magneticfield location.
 2. The device of claim 1, wherein the manipulation ofthe magnetic target object is chosen from enrichment, capture, sorting,separation, concentration within a selected region of the biofluid, orany combination thereof of the target object within the area ofinterest.
 3. The device of claim 1, wherein the at least one magnet issituated at a distance between about 0.1 mm and about 20 cm from thearea of interest.
 4. The device of claim 1, wherein the device detectsthe magnetic target object at a detection sensitivity ranging from about1 to about 100 target objects per L of the moving biofluid.
 5. Thedevice of claim 1, wherein the at least one magnet produces a field thatcaptures the magnetic target object within the area of interest.
 6. Thedevice of claim 1, wherein the moving biofluid is chosen from blood,lymph, cerebrospinal fluid, urine, chyme, cytosol, tears, orinterstitial fluid.
 7. The device of claim 1, wherein the magnetictarget object is chosen from an intrinsically magnetic target object ora target object labeled with a magnetic particle.
 8. The device of claim7, wherein the magnetic particle is chosen from a magnetic nanoparticleor a magnetic microparticle having a size ranging from about 5 nm toabout 10 μm.
 9. The device of claim 1, wherein the magnetic targetobject is labeled with a contrast agent selected from an ultrasoundcontrast agent, a photoacoustic contrast agent, a hybrid contrast agent,a fluorescent contrast agent, a Raman contrast agent, an MRI contrastagent, a superconductivity quantum interference device contrast agent, aPET contrast agent, and a CT contrast agent.
 10. The device of claim 9,wherein the hybrid contrast agent is a nanoparticle complex or amicroparticle complex chosen from a gold-magnetic complex, a quantumdot-magnetic complex, a carbon nanotube-magnetic complex, aradionucleotide-magnetic complex, a surface enhanced resonancescattering-magnetic complex, or any combination thereof.
 11. The deviceof claim 1, wherein the magnetic field has a strength ranging from about0.1 T to about 20 T.
 12. The device of claim 11, wherein the magneticfield is chosen from a permanent field and a pulsed field.
 13. Thedevice of claim 1, wherein the at least one magnet comprises two or moremagnets situated along a direction of movement of the moving biofluid.14. The device of claim 13, further comprising a securing cuff includingthe two or more magnets.
 15. The device of claim 1, wherein at least onemagnet is configured to be in contact with the external integument ofthe living organism.
 16. The device of claim 15, further comprising amagnetic cuff including the at least one magnet.
 17. The device of claim1, wherein the at least one magnet is configured to be invasivelysituated in the vicinity of the moving biofluid.
 18. The device of claim17, further comprising an invasive insertion device chosen from a needleor a catheter, wherein the invasive insertion device includes the atleast one magnet.
 19. The device of claim 1, further comprising anextracorporeal shunt including a circulatory bypass tube forcontinuously withdrawing the moving biofluid out of the living organism,directing the moving biofluid through the circulatory bypass tube, andreturning the moving biofluid back into the organism, wherein the areaof interest includes a cross-section of the circulatory bypass tube. 20.A method of manipulating and detecting magnetic target objects within amoving biofluid of a living organism, comprising: situating at least onemagnet to manipulate the magnetic target objects within a magnetic fieldproduced by the at least one magnet in an area of interest; anddetecting the magnetic target objects using an in vivo flow cytometerwherein the in vivo flow cytometer is an in vivo photoacoustic flowcytometer comprising a laser fiber for delivering at least one laserpulse to the area of interest, wherein the laser fiber comprises afocusing tip to transmit the at least one laser pulse to the area ofinterest; and wherein the at least one magnet comprises a magneticmaterial forming a channel, wherein the laser fiber passes through thechannel and the focusing tip is situated at a laser pulse location thatis essentially coincident to a corresponding magnetic field location.21. The method of claim 20, wherein the manipulation of the magnetictarget objects is chosen from enrichment, capture, sorting, separation,concentration within a selected region of the biofluid, or anycombination thereof of the target objects within the area of interest.22. The method of claim 20, wherein the at least one magnet is situatedat a distance between about 0.1 mm and about 20 cm from the area ofinterest.
 23. The method of claim 20, wherein the device detects themagnetic target objects at a detection sensitivity ranging from about 1to about 100 target objects per L of the moving biofluid.
 24. The methodof claim 20, wherein the at least one magnet produces a field thatcaptures the magnetic target objects within the area of interest. 25.The method of claim 20, wherein the moving biofluid is chosen fromblood, lymph, cerebrospinal fluid, urine, chyme, cytosol, tears, orinterstitial fluid.
 26. The method of claim 20, wherein the magnetictarget objects are chosen from intrinsically magnetic target objects ortarget objects labeled with magnetic particles.
 27. The method of claim26, further comprising labeling target objects with magnetic particlesto obtain the target objects labeled with magnetic particles.
 28. Themethod of claim 27, wherein the target objects are additionally labeledwith contrast agents chosen from ultrasound contrast agents,photoacoustic contrast agents, hybrid contrast agents, fluorescentcontrast agents, Raman contrast agents, MRI contrast agents,superconductivity quantum interference device contrast agents, PETcontrast agents, or CT contrast agents.
 29. The method of claim 28,wherein the hybrid contrast agents are nanoparticle complexes or amicroparticle complexes chosen from gold-magnetic complexes, quantumdot-magnetic complexes, carbon nanotube-magnetic complexes,radionucleotide-magnetic complexes, surface enhanced resonancescattering-magnetic complexes, or any combination thereof.
 30. Themethod of claim 28, wherein the contrast agents used to additionallylabel the target objects are conjugated with second targeting moietieschosen from antibodies, ligands, antigens, or cell marker proteins,wherein the second targeting moieties are different from the firsttargeting moieties.
 31. The method of claim 30, further comprisinginjecting the conjugated contrast agent into the moving biofluid priorto situating the at least one magnet.
 32. The method of claim 26,wherein the magnetic particles are chosen from magnetic nanoparticles ormagnetic microparticles having a size ranging from about 5 nm to about10 μm.
 33. The method of claim 26, wherein the magnetic particles usedto label the target objects comprise magnetic nanoparticles conjugatedwith first targeting moieties chosen from antibodies, ligands, antigens,or cell marker proteins.
 34. The method of claim 33, further comprisinginjecting the magnetic particles conjugated with targeting moieties intothe moving biofluid prior to situating the at least one magnet.
 35. Themethod of claim 26, wherein the target objects are labeled with magneticparticles and the target objects are chosen from biomarkers, drugs,toxins, microparticles, nanoparticles, viruses, or cells.
 36. The methodof claim 35, wherein the biomarkers are chosen from proteins,antibodies, hormones, single-stranded DNA fragments, double-stranded DNAfragments, or RNA fragments.
 37. The method of claim 35, wherein thecells are chosen from pathogenic bacteria, pathogenic fungi, pathogenicprotists, or cancer cells.
 38. The method of claim 37, wherein thecancer cells are metastatic cancer stem cells resulting from a cancerchosen from melanoma, leukemia, brain cancer, breast cancer, coloncancer, prostate cancer, ovarian cancer, pancreatic cancer, ortesticular cancer.
 39. The method of claim 20, wherein the movingbiofluid flows through a circulatory vessel chosen from a blood vessel,a lymphatic vessel, an extracorporeal shunt, or any combination thereof.40. The method of claim 39, wherein the at least one magnet isinvasively situated in the vicinity of the circulatory vessel.
 41. Themethod of claim 40, wherein the at least one magnet is incorporated intoan invasive insertion device chosen from a needle device or a catheterdevice.
 42. The method of claim 20, further comprising subjecting thedetected magnetic target objects to an additional process chosen fromremoval for biochemical or genetic analysis; non-invasive eradicationusing high-energy pulses chosen from laser pulses, microwave pulses, orultrasound pulses; magnetic purging; mechanical removal; needleextraction; or any combination thereof.
 43. A method of detecting thepresence of target cells within a biofluid of a living organism movingthrough a circulatory vessel, comprising: injecting magneticnanoparticles conjugated with first targeting moieties into thecirculatory vessel to produce magnetic target cells comprising themagnetic particles attached to the target cells; injecting photoacousticcontrast agents conjugated with second targeting moieties different thanthe first targeting moieties into the circulatory vessel producingmagnetic target cells labeled with the photoacoustic contrast agents;situating at least one magnet to manipulate the magnetic target cellswithin a magnetic field produced in an area of interest by the at leastone magnet; detecting the magnetic target cells in the area of interestusing an in vivo photoacoustic flow cytometer; and, subjecting themagnetic target cells to an additional process chosen from removal forbiochemical or genetic analysis; non-invasive eradication usinghigh-energy pulses chosen from laser pulses, microwave pulses, orultrasound pulses; magnetic purging; mechanical removal; needleextraction; or any combination thereof.
 44. The method of claim 43,wherein the manipulation of the magnetic target cells is chosen fromenrichment, capture, sorting, separation, concentration within aselected region of the biofluid, or any combination thereof of themagnetic target cells within the area of interest.
 45. The method ofclaim 43, wherein the at least one magnet produces a field that capturesthe magnetic target cells within the circulatory vessel.
 46. The methodof claim 43, wherein the at least one magnet is situated at a distanceranging from about 0.1 mm to about 20 cm from the area of interest. 47.The method of claim 43, wherein the first targeting moieties and thesecond targeting moieties are chosen from antibodies, ligands, antigens,or cell marker proteins.
 48. The method of claim 43, wherein the movingbiofluid is chosen from blood, lymph, cerebrospinal fluid, urine, chyme,cytosol, tears, or interstitial fluid.
 49. The method of claim 43,wherein the target cells are chosen from abnormal cells chosen fromsickle cells, inflamed cells, or cancer cells; pathogenic bacteria;pathogenic fungal cells; or pathogenic protists.
 50. The method of claim49, wherein the cancer cells are metastatic cancer stem cells resultingfrom a cancer chosen from melanoma, leukemia, brain cancer, breastcancer, colon cancer, prostate cancer, ovarian cancer, pancreaticcancer, or testicular cancer.